AArch64: enable new predicate tuning for Neoverse cores.

This enables the new tuning flag for Neoverse V1, Neoverse V2 and Neoverse N2.
It is kept off for generic codegen.

Note the reason for the +sve even though they are in aarch64-sve.exp is if the
testsuite is ran with a forced SVE off option, e.g. -march=armv8-a+nosve then
the intrinsics end up being disabled because the -march is preferred over the
-mcpu even though the -mcpu comes later.

This prevents the tests from failing in such runs.

gcc/ChangeLog:

	* config/aarch64/tuning_models/neoversen2.h (neoversen2_tunings): Add
	AARCH64_EXTRA_TUNE_AVOID_PRED_RMW.
	* config/aarch64/tuning_models/neoversev1.h (neoversev1_tunings): Add
	AARCH64_EXTRA_TUNE_AVOID_PRED_RMW.
	* config/aarch64/tuning_models/neoversev2.h (neoversev2_tunings): Add
	AARCH64_EXTRA_TUNE_AVOID_PRED_RMW.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/pred_clobber_1.c: New test.
	* gcc.target/aarch64/sve/pred_clobber_2.c: New test.
	* gcc.target/aarch64/sve/pred_clobber_3.c: New test.
	* gcc.target/aarch64/sve/pred_clobber_4.c: New test.