aarch64: specify fpm mode in function instances and groups

aarch64: specify fpm mode in function instances and groups

Some intrinsics require setting the fpm register before calling the
specific asm opcode required.
In order to simplify review, this patch:
- adds the fpm_mode_index attribute to function_group_info and
  function_instance objects
- updates existing initialisations and call sites.
- updates equality and hash operations

gcc/
	* config/aarch64/aarch64-sve-builtins-base.cc
	(svdiv_impl): Specify FPM_unused when folding.
	(svmul_impl): Likewise.
	* config/aarch64/aarch64-sve-builtins-shapes.cc
	(build_one): Use the group fpm_mode when creating function instances.
	* config/aarch64/aarch64-sve-builtins-sve2.cc
	(svaba_impl, svqrshl_impl, svqshl_impl,svrshl_impl, svsra_impl):
	Specify FPM_unused when folding.
	* config/aarch64/aarch64-sve-builtins.cc (function_groups): Set
	fpm_mode on all elements.
	(neon_sve_function_groups, sme_function_groups): Likewise.
	(function_instance::hash): Include fpm_mode in hash.
	(function_builder::add_overloaded_functions): Use the group fpm mode.
	(function_resolver::lookup_form): Use the function instance fpm_mode
	when looking up a function.
	* config/aarch64/aarch64-sve-builtins.def
	(DEF_SVE_FUNCTION_GS_FPM): add define.
	(DEF_SVE_FUNCTION_GS): redefine against DEF_SVE_FUNCTION_GS_FPM.
	* config/aarch64/aarch64-sve-builtins.h (fpm_mode_index): New.
	(function_group_info): Add fpm_mode.
	(function_instance): Likewise.
	(function_instance::operator==): Handle fpm_mode.