- Adds the concept of FP register aliasing to RegisterConfiguration.
- Changes RegisterAllocator to distinguish between FP representations
when allocating.
- Changes LinearScanAllocator to detect interference when FP register
aliasing is combining, as on ARM.
- Changes ARM code generation to allow all registers s0 - s31 to be
accessed.
- Adds unit tests for RegisterConfiguration, mostly to test aliasing
calculations.

LOG=N
BUG=v8:4124

Review-Url: https://codereview.chromium.org/2086653003
Cr-Commit-Position: refs/heads/master@{#37251}