Functions/variables for some atomic memory operators use type,
representation interchangeably. Fix to make it consistent.

Bug: v8:7754, v8:6532
Change-Id: I16ae35b72728739aee4bc67287317c2fd4a9088a
Reviewed-on: https://chromium-review.googlesource.com/1152462Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54763}