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

[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.

llvm-svn: 284912