AVX512FP16: Enhance vector shuffle builtins

AVX512FP16: Enhance vector shuffle builtins

Support HFmode vector shuffle by creating HImode subreg when
expanding permutation expr.

gcc/ChangeLog:

	* config/i386/i386-expand.c (ix86_expand_vec_perm): Convert
	HFmode input operand to HImode.
	(ix86_vectorize_vec_perm_const): Likewise.
	* config/i386/sse.md (*avx512bw_permvar_truncv16siv16hi_1_hf):
	New define_insn.
	(*avx512f_permvar_truncv8siv8hi_1_hf):
	Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/avx512fp16-builtin_shuffle-1.c: New test.
	* gcc.target/i386/avx512fp16-pr101846.c: Ditto.
	* gcc.target/i386/avx512fp16-pr94680.c: Ditto.