Split X86_TUNE_AVX128_OPTIMAL into X86_TUNE_AVX256_SPLIT_REGS

Split X86_TUNE_AVX128_OPTIMAL into X86_TUNE_AVX256_SPLIT_REGS
and X86_TUNE_AVX128_OPTIMAL.

Changelog
gcc/
	PR target/92448
	* config/i386/i386-expand.c (ix86_expand_set_or_cpymem):
	Replace TARGET_AVX128_OPTIMAL with TARGET_AVX256_SPLIT_REGS.
	* config/i386/i386-option.c (ix86_vec_cost): Ditto.
	(ix86_reassociation_width): Ditto.
	* config/i386/i386-options.c (ix86_option_override_internal):
	Replace TARGET_AVX128_OPTIAML with
	ix86_tune_features[X86_TUNE_AVX128_OPTIMAL]
	* config/i386/i386.h (TARGET_AVX256_SPLIT_REGS): New macro.
	(TARGET_AVX128_OPTIMAL): Deleted.
	* config/i386/x86-tune.def (X86_TUNE_AVX256_SPLIT_REGS): New
	DEF_TUNE.

From-SVN: r278385