i386: Utilize VCOMSBF16 for BF16 Comparisons with AVX10.2

i386: Utilize VCOMSBF16 for BF16 Comparisons with AVX10.2

This patch enables the use of the VCOMSBF16 instruction from AVX10.2 for
efficient BF16 comparisons.

gcc/ChangeLog:

	* config/i386/i386-expand.cc (ix86_expand_branch): Handle BFmode
	when TARGET_AVX10_2_256 is enabled.
	(ix86_prepare_fp_compare_args): Use SSE_FLOAT_MODE_SSEMATH_OR_HFBF_P.
	(ix86_expand_fp_movcc): Ditto.
	(ix86_expand_fp_compare): Handle BFmode under IX86_FPCMP_COMI.
	* config/i386/i386.cc (ix86_multiplication_cost): Use
	SSE_FLOAT_MODE_SSEMATH_OR_HFBF_P.
	(ix86_division_cost): Ditto.
	(ix86_rtx_costs): Ditto.
	(ix86_vector_costs::add_stmt_cost): Ditto.
	* config/i386/i386.h (SSE_FLOAT_MODE_SSEMATH_OR_HF_P): Rename to ...
	(SSE_FLOAT_MODE_SSEMATH_OR_HFBF_P): ...this, and add BFmode.
	* config/i386/i386.md (*cmpibf): New define_insn.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx10_2-comibf-1.c: New test.
	* gcc.target/i386/avx10_2-comibf-2.c: Ditto.