- Changes x64 AssembleSwap to push/pop to swap 128 bit slot swaps.
- Reorders instructions to simplify 32/64 bit FP slot swaps.
- Refactor ia32 version of this, eliminating OffsetOperand in favor of
  existing ToOperand.

Bug: v8:6020
Change-Id: Ie0ae4c581c9aeb88ee786797851c3c77d5210a3d
Reviewed-on: https://chromium-review.googlesource.com/669748
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48096}