i386: vcvtph2ps and vcvtps2ph should be used to convert _Float16 to SFmode with ...

i386: vcvtph2ps and vcvtps2ph should be used to convert _Float16 to SFmode with -mf16c [PR 102811]

Add define_insn extendhfsf2 and truncsfhf2 for target_f16c.

gcc/ChangeLog:

	PR target/102811
	* config/i386/i386.c (ix86_can_change_mode_class): Allow 16 bit data in XMM register
	for TARGET_SSE2.
	* config/i386/i386.md (extendhfsf2): Add extenndhfsf2 for TARGET_F16C.
	(extendhfdf2): Restrict extendhfdf for TARGET_AVX512FP16 only.
	(*extendhf<mode>2): Rename from extendhf<mode>2.
	(truncsfhf2): Likewise.
	(truncdfhf2): Likewise.
	(*trunc<mode>2): Likewise.

gcc/testsuite/ChangeLog:

	PR target/102811
	* gcc.target/i386/pr90773-21.c: Allow pextrw instead of movw.
	* gcc.target/i386/pr90773-23.c: Ditto.
	* gcc.target/i386/avx512vl-vcvtps2ph-pr102811.c: New test.