[x86] Clean up the shift lowering vector shuffle tests a bit using my

[x86] Clean up the shift lowering vector shuffle tests a bit using my
script. Notably this folds all the SSE cases together into a single
FileCheck block. It also adds a vex prefix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223610 91177308-0d34-0410-b5e6-96231b3b80d8