[X86] Refactor some of the X86 autoupgrade code to split mask vector and select generation into routines that can be reused for future intrinsic upgrades. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272526 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed