Aarch64: Func to detect args passed in float regs

Aarch64: Func to detect args passed in float regs

aapcs_is_vfp_call_or_return_candidate is as an eventual replacement
for is_hfa_or_hva.

This function is based on the GCC code
gcc/config/aarch64/aarch64.c:aarch64_vfp_is_call_or_return_candidate ()

gdb/
	* aarch64-tdep.c (HA_MAX_NUM_FLDS): New macro.
	(aapcs_is_vfp_call_or_return_candidate_1): New function.
	(aapcs_is_vfp_call_or_return_candidate): Likewise.