UnalignedLoad is the only kind of load operation that defines its own
UnalignedLoadRepresentation type alias and LoadRepresentationOf function.
This is a problem because it means we cannot use the LOAD_MATCHER
infrastructure without defining all of this boilerplate for all the other
kinds of load operations. Since these aliases serve no real purpose,
it is best to unify UnalignedLoad to how its peers are handled.

Change-Id: I51a591eb82fb85edee66512136b23276e851f767
Reviewed-on: https://chromium-review.googlesource.com/951683
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51802}