[X86][AVX512BW] Fixed 512-bit PSHUFB shuffle mask decode and added combine test.

PSHUFB decoder was assuming that input was 128 or 256-bit vector only.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262661 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed