Reconstruct pshufb using macro

Bug: 
Change-Id: I5556ce1108378fc7a7658443cd09c3f676c16aa7
Reviewed-on: https://chromium-review.googlesource.com/603907Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47228}