This syncs the dmc clk rate change with vblank. BUG=chrome-os-partner:31440 TEST=boot pinky Signed-off-by: Derek Basehore <dbasehore@chromium.org> Change-Id: I6f1d5975548e83d2baf1242fa95a5df5dde7c7a9 Reviewed-on: https://chromium-review.googlesource.com/231478 Reviewed-by: Andrew Bresticker <abrestic@chromium.org> Tested-by: Derek Basehore <dbasehore@google.com> Commit-Queue: Derek Basehore <dbasehore@google.com> Trybot-Ready: Derek Basehore <dbasehore@google.com>