Moves between operands with different representations shouldn't happen,
so don't test them. This makes it easier to modify canonicalization to
differentiate between floating point types, which is needed to support
floating point register aliasing for ARM and MIPS.

This change also expands tests to include explicit FP moves (both register and stack slot).

LOG=N
BUG=v8:4124

Review-Url: https://codereview.chromium.org/2060273003
Cr-Commit-Position: refs/heads/master@{#36963}