[AArch64][2/14] Refactor arches handling, add arch enum identifier

[AArch64][2/14] Refactor arches handling, add arch enum identifier

	* config/aarch64/aarch64.h (TARGET_CPU_CPP_BUILTINS): Define
	__ARM_ARCH_8A directly rather than with cpp_define_formatted.
	* config/aarch64/aarch64.c (struct processor): Add arch field.
	(all_architectures): Handle above, move above all_cores.
	(all_cores): Handle above.
	(aarch64_parse_arch): Handle above changes.
	* config/aarch64/aarch64-arches.def (armv8-a): Extend according to
	above.  Update comments.
	(armv8.1-a): Likewise.
	* config/aarch64/aarch64-cores.def: Update according to above.
	* config/aarch64/aarch64-opts.h (aarch64_arch): New enum.
	* config/aarch64/driver-aarch64.c (struct aarch64_arch): Rename to
	aarch64_arch_driver_info.

From-SVN: r226553