i386: Disable ix86_expand_vecop_qihi2 when !TARGET_AVX512BW

i386: Disable ix86_expand_vecop_qihi2 when !TARGET_AVX512BW

Since vpermq is really slow, we should avoid using it for permutation
when vpmovwb is not available (needs AVX512BW) for ix86_expand_vecop_qihi2
and fall back to ix86_expand_vecop_qihi.

gcc/ChangeLog:

	PR target/115069
	* config/i386/i386-expand.cc (ix86_expand_vecop_qihi2):
	Do not enable the optimization when AVX512BW is not enabled.

gcc/testsuite/ChangeLog:

	PR target/115069
	* gcc.target/i386/pr115069.c: New.