[X86][SSE] Add support for combining SSE VSHLI/VSRLI uniform constant shifts.

Fixes some missed constant folding opportunities and allows us to combine shuffles that end with a logical bit shift.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289429 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed