When we don't have a base, and the displacement returned by the
BaseWithIndexAndDisplacement64Matcher cannot be encoded as immediate,
we can still try to utilize the scale factor matching by just using
the displacement as base. This happens when we do indexed memory
accesses to known addresses.

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2504123002
Cr-Commit-Position: refs/heads/master@{#41016}