- Adds v/pshufhw, v/palignr instructions to assembler and
  macro-assembler.
- Uses better instruction sequences for 32x4 shuffles using half-
  shuffles and blends.
- Uses better instruction sequences for 16x8 shuffles.
- Uses better instruction sequences for concatenating 8x16 shuffles.

Change-Id: I3e6dca2937a2b167c754c47331c3a2f8ab9786db
Reviewed-on: https://chromium-review.googlesource.com/1066986
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53460}