x86: Handle V16BF in ix86_avx256_split_vector_move_misalign

Handle E_V16BFmode in ix86_avx256_split_vector_move_misalign and add
V16BF to V_256H iterator.

gcc/

	PR target/106748
	* config/i386/i386-expand.cc
	(ix86_avx256_split_vector_move_misalign): Handle E_V16BFmode.
	* config/i386/sse.md (V_256H): Add V16BF.

gcc/testsuite/

	PR target/106748
	* gcc.target/i386/pr106748.c: New test.