[X86][FP16] Fix vector_shuffle and lowering without f16c feature problems

The problem Alexander reported on D127982 was caused by an optimization
for AVX512-FP16 instruction. We must limit it to the feature enabled only.

During the investigation, I found we didn't expand for fp_round/fp_extend
without F16C. This may result runtime crash, so change them too.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D130817