[X86][AVX] Enable shuffle combining support for zero_extend

A more limited version of rL352997 that had to be disabled in rL353198 - allow extension of any 128/256/512 bit vector that at least uses byte sized scalars.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@353860 91177308-0d34-0410-b5e6-96231b3b80d8