aarch64, Darwin: Initial implementation of Apple cores [PR113257].

aarch64, Darwin: Initial implementation of Apple cores [PR113257].

After discussion with the open source support team at Apple, we have
established that the cores conform to the 8.5 and 8.6 requirements.
One of the mandatory features (FEAT_SPECRES) is not exposed (or
available) in user-space code but is supported for privileged code.

The values for chip IDs and the LITTLE.big variants have been taken
from lists in the XNU and LLVM sources.

	PR target/113257

gcc/ChangeLog:

	* config/aarch64/aarch64-cores.def (AARCH64_CORE): Add Apple-a12,
	Apple-M1, Apple-M2, Apple-M3 with expanded names to allow for the
	LITTLE.big versions.
	* config/aarch64/aarch64-tune.md: Regenerate.
	* doc/invoke.texi: Add apple-m1,2 and 3 cores to the ones listed
	for arch and tune selections.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>