vulkan: optimizations for deepseek prompt processing

[jeffbolznv]

Some optimizations for mul_mat_id, and flash attention with large head size. See commit messages for more detail.

before:

coopmat2:

Z:\github\jeffbolznv\llama.cpp\build\bin\RelWithDebInfo>llama-bench -m C:\models\deepseek-v2-lite-safetensors\deepseek-v2-lite-Q4_K_M.gguf -fa 1 -n 128 -p 512 -d 512,8192 --prio 1 -r 5
ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = NVIDIA GeForce RTX 5090 (NVIDIA) | uma: 0 | fp16: 1 | warp size: 32 | shared memory: 49152 | int dot: 1 | matrix cores: NV_coopmat2
| model                          |       size |     params | backend    | ngl | fa |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | --: | -: | --------------: | -------------------: |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    pp512 @ d512 |      4061.98 ± 17.67 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    tg128 @ d512 |        210.15 ± 0.88 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   pp512 @ d8192 |      2392.49 ± 16.93 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   tg128 @ d8192 |        116.90 ± 0.26 |

coopmat1:

Z:\github\jeffbolznv\llama.cpp\build\bin\RelWithDebInfo>llama-bench -m C:\models\deepseek-v2-lite-safetensors\deepseek-v2-lite-Q4_K_M.gguf -fa 1 -n 128 -p 512 -d 512,8192 --prio 1 -r 1
ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = NVIDIA GeForce RTX 5090 (NVIDIA) | uma: 0 | fp16: 1 | warp size: 32 | shared memory: 49152 | int dot: 1 | matrix cores: KHR_coopmat
| model                          |       size |     params | backend    | ngl | fa |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | --: | -: | --------------: | -------------------: |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    pp512 @ d512 |       1013.83 ± 0.00 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    tg128 @ d512 |        203.44 ± 0.00 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   pp512 @ d8192 |        159.70 ± 0.00 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   tg128 @ d8192 |        151.71 ± 0.00 |

scalar:

Z:\github\jeffbolznv\llama.cpp\build\bin\RelWithDebInfo>llama-bench -m C:\models\deepseek-v2-lite-safetensors\deepseek-v2-lite-Q4_K_M.gguf -fa 1 -n 128 -p 512 -d 512,8192 --prio 1 -r 1
ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = NVIDIA GeForce RTX 5090 (NVIDIA) | uma: 0 | fp16: 1 | warp size: 32 | shared memory: 49152 | int dot: 1 | matrix cores: none
| model                          |       size |     params | backend    | ngl | fa |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | --: | -: | --------------: | -------------------: |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    pp512 @ d512 |        868.16 ± 0.00 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    tg128 @ d512 |        202.75 ± 0.00 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   pp512 @ d8192 |        161.14 ± 0.00 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   tg128 @ d8192 |        151.54 ± 0.00 |

after:

coopmat2:

Z:\github\jeffbolznv\llama.cpp\build\bin\RelWithDebInfo>llama-bench -m C:\models\deepseek-v2-lite-safetensors\deepseek-v2-lite-Q4_K_M.gguf -fa 1 -n 128 -p 512 -d 512,8192 --prio 1 -r 5
ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = NVIDIA GeForce RTX 5090 (NVIDIA) | uma: 0 | fp16: 1 | warp size: 32 | shared memory: 49152 | int dot: 1 | matrix cores: NV_coopmat2
| model                          |       size |     params | backend    | ngl | fa |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | --: | -: | --------------: | -------------------: |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    pp512 @ d512 |      6419.30 ± 17.34 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    tg128 @ d512 |        209.36 ± 0.86 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   pp512 @ d8192 |      3606.39 ± 10.05 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   tg128 @ d8192 |        116.51 ± 0.28 |

coopmat1:

Z:\github\jeffbolznv\llama.cpp\build\bin\RelWithDebInfo>llama-bench -m C:\models\deepseek-v2-lite-safetensors\deepseek-v2-lite-Q4_K_M.gguf -fa 1 -n 128 -p 512 -d 512,8192 --prio 1 -r 5
ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = NVIDIA GeForce RTX 5090 (NVIDIA) | uma: 0 | fp16: 1 | warp size: 32 | shared memory: 49152 | int dot: 1 | matrix cores: KHR_coopmat
| model                          |       size |     params | backend    | ngl | fa |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | --: | -: | --------------: | -------------------: |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    pp512 @ d512 |      5412.19 ± 58.07 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    tg128 @ d512 |        202.60 ± 0.77 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   pp512 @ d8192 |       1630.19 ± 3.38 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   tg128 @ d8192 |        151.86 ± 0.46 |

scalar:

Z:\github\jeffbolznv\llama.cpp\build\bin\RelWithDebInfo>llama-bench -m C:\models\deepseek-v2-lite-safetensors\deepseek-v2-lite-Q4_K_M.gguf -fa 1 -n 128 -p 512 -d 512,8192 --prio 1 -r 5
ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = NVIDIA GeForce RTX 5090 (NVIDIA) | uma: 0 | fp16: 1 | warp size: 32 | shared memory: 49152 | int dot: 1 | matrix cores: none
| model                          |       size |     params | backend    | ngl | fa |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | --: | -: | --------------: | -------------------: |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    pp512 @ d512 |       1833.69 ± 7.71 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |    tg128 @ d512 |        204.14 ± 0.45 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   pp512 @ d8192 |       1034.34 ± 1.45 |
| deepseek2 16B Q4_K - Medium    |   9.65 GiB |    15.71 B | Vulkan     |  99 |  1 |   tg128 @ d8192 |        151.88 ± 0.27 |