- Cleans up existing code that tests for representations using a
  bitmask.
- Bypass FP register allocation for sequences without FP vregs.

Change-Id: I5ff32e80e0c33848ba83ee17f786b01e37821aa2
Reviewed-on: https://chromium-review.googlesource.com/1195528
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55535}