Optimize V16HF vector insert to element 0 for AVX2.

Optimize V16HF vector insert to element 0 for AVX2.

gcc/ChangeLog:

	PR target/103753
	* config/i386/i386-expand.c (ix86_expand_vector_set): Not use
	gen_avx2_pblendph_1 when elt == 0.
	* config/i386/sse.md (avx2_pblendph): Rename to ..
	(avx2_pblend<ssemodesuffix>_1).. this, and extend to V16HI.
	(*avx2_pblendw): Rename to ..
	(*avx2_pblend<ssemodesuffix>): .. this, and extend to V16HF.
	(avx2_pblendw): Rename to ..
	(*avx2_pblend<ssemodesuffix>): .. this, and extend to V16HF.
	(blendsuf): Removed.
	(sse4_1_pblend<blendsuf>): Renamed to ..
	(sse4_1_pblend<ssemodesuffix>): .. this.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr103753.c: New test.