aarch64: Split sve2-X extensions into sve2 + sve-X extension.

aarch64: Split sve2-X extensions into sve2 + sve-X extension.

Changes the "sve2-sm4", "sve2-sha3", "sve2-bitperm", and "sve2-aes"
to be aliases which imply both "sve2" and the new option "sve-sm4",
"sve-sha3", "sve-bitperm", or "sve-aes" respectively.

The EXPLICIT_OFF values are chosen to preserve the existing behaviour of
+nosve2-X.

This granularity is needed to model the 2024 Architecture Extensions
dependencies.

gcc/ChangeLog:

	* config/aarch64/aarch64-option-extensions.def
	(sve-aes): New cli extension option.
	(sve2-aes): Changed to be alias of sve2+sve-aes2.
	(sve-bitperm): New cli extension option.
	(sve2-bitperm): Changed to be alias of sve2+sve-bitperm.
	(sve-sm4): New cli extension option.
	(sve2-sm4): Changed to be alias of sve2+sve-sm4.
	(sve-sm4): New cli extension option.
	(sve2-sm4): Changed to be alias of sve2+sve-sm4.
	* config/aarch64/aarch64.h (TARGET_SVE2_AES): Updated to require
	sve2+sve-aes.
	(TARGET_SVE2_BITPERM): Updated to require sve2+sve-bitperm.
	(TARGET_SVE2_SHA3): Updated to require sve2+sve-sha3.
	(TARGET_SVE2_SM4): Updated to require sve2+sve-sm4
	* config/aarch64/aarch64-sve-builtins-sve2.def: Update gating for sve2-X
	intrinsics.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/pragma_cpp_predefs_5.c: New test.
	* gcc.target/aarch64/options_set_30.c: Likewise.
	* lib/target-supports.exp (exts): Add sve-sm4, sve-aes, sve-bitperm.