Hi all,

This patch adds the +mops architecture extension flag from the 2021 Arm Architecture extensions, Armv8.8-a.
The +mops extensions introduce instructions to accelerate the memcpy, memset, memmove standard functions.
The first patch here uses the instructions in the inline memcpy expansion.
Further patches in the series will use similar instructions to inline memmove and memset.

A new param, aarch64-mops-memcpy-size-threshold, is introduced to control the size threshold above which to
emit the new sequence. Its default setting is 256 bytes, which is the same as the current threshold above
which we'd emit a libcall.

Bootstrapped and tested on aarch64-none-linux-gnu.
Pushing to trunk.
Thanks,
Kyrill

gcc/ChangeLog:

	* config/aarch64/aarch64-option-extensions.def (mops): Define.
	* config/aarch64/aarch64.c (aarch64_expand_cpymem_mops): Define.
	(aarch64_expand_cpymem): Define.
	* config/aarch64/aarch64.h (AARCH64_FL_MOPS): Define.
	(AARCH64_ISA_MOPS): Define.
	(TARGET_MOPS): Define.
	(MOVE_RATIO): Adjust for TARGET_MOPS.
	* config/aarch64/aarch64.md ("unspec"): Add UNSPEC_CPYMEM.
	(aarch64_cpymemdi): New pattern.
	(cpymemdi): Adjust for TARGET_MOPS.
	* config/aarch64/aarch64.opt (aarch64-mops-memcpy-size-threshol):
	New param.
	* doc/invoke.texi (AArch64 Options): Document +mops.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/mops_1.c: New test.