added boot/amd-ucode.img to pacman hook

just plain `cp` /proc/cmdline

this removes the bash-ism
```
`< …`
```

allow /etc/kernel/cmdline to have newlines

newlines in /etc/kernel/cmdline are replaced with spaces

add back SUFFIX var for backward compatibility

added fwupd hook

added kernel-install hook

https://www.freedesktop.org/software/systemd/man/kernel-install.html

support config file and other small updates:

* support specifing the boot device for efibootmgr

Some of the options that can be specified (and their defaults):
```
ESP    = /boot
EFIDIR = /EFI/Secure
EFIBOOTDEVICE =

SIGNER = ArchSecureBoot
SUFFIX = linux
UCODE = /boot/intel-ucode.img
```

initial commit