[X86] Remove 128-bit lane handling from the main loop of matchVectorShuffleAsByteRota...

[X86] Remove 128-bit lane handling from the main loop of matchVectorShuffleAsByteRotate. Instead check for is128LaneRepeatedSuffleMask before the loop and just loop over the repeated mask.

I plan to use the loop to support VALIGND/Q shuffles so this makes it easier to reuse.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@284912 91177308-0d34-0410-b5e6-96231b3b80d8