For binary operations and unary operations, we were pinning too many
registers, thereby disallowing to reuse a src register for the result.

R=ahaas@chromium.org

Bug: v8:6600
Change-Id: Id4eea1e35d29c170e191249ef42d11ed1d284490
Reviewed-on: https://chromium-review.googlesource.com/1021818Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52720}