AVX512FP16: Add vmovw/vmovsh.

gcc/ChangeLog:

	* config/i386/avx512fp16intrin.h: (_mm_cvtsi16_si128):
	New intrinsic.
	(_mm_cvtsi128_si16): Likewise.
	(_mm_mask_load_sh): Likewise.
	(_mm_maskz_load_sh): Likewise.
	(_mm_mask_store_sh): Likewise.
	(_mm_move_sh): Likewise.
	(_mm_mask_move_sh): Likewise.
	(_mm_maskz_move_sh): Likewise.
	* config/i386/i386-builtin-types.def: Add corresponding builtin types.
	* config/i386/i386-builtin.def: Add corresponding new builtins.
	* config/i386/i386-expand.c
	(ix86_expand_special_args_builtin): Handle new builtin types.
	(ix86_expand_vector_init_one_nonzero): Adjust for FP16 target.
	* config/i386/sse.md (VI2F): New mode iterator.
	(vec_set<mode>_0): Use new mode iterator.
	(avx512f_mov<ssescalarmodelower>_mask): Adjust for HF vector mode.
	(avx512f_store<mode>_mask): Ditto.