A minor optimization to the four bit rotation functions.

Drive-by: Make them constexpr.

R=ahaas@chromium.org

Bug: v8:9810
Change-Id: Ic563310030aa487f976017032291a553705d1ec2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1903972Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64854}