[GDBserver] Add support for Z0 packets

[shahab-vahedi]

Z0 packets in remote debugging sessions are for inserting (software) breakpoints. Currently, ARC GDB client inserts a breakpoint by writing the opcodes to memory through GDBserver (see these).

Remarks:

• Z0 is the modern way that provides more features (like target-side condition
  evaluation) and a memory write is the legacy fallback.
• sw_breakpoint_from_kind would be used if the Z0 packet was used, to translate the kind into an opcode.
• The input for sw_breakpoint_from_kind can come from the Z0 packet
• The ARC port doesn't implement low_insert_point and low_remove_point. That's probably why it falls back to inserting breakpoint with writing to memory.