CHROMIUM: add page flip to cirrus drm

BUG=None
TEST=Run `modetest -M cirrus -s 19:800x600 -v` under qemu and make sure
the page flips

Signed-off-by: Zach Reizner <zachr@chromium.org>
Change-Id: Ifb6f9795063e11c7c5706780ff6f73c0d8e15562
Reviewed-on: https://chromium-review.googlesource.com/223794
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Merge branch 'chromeos-3.8' of https://chromium.googlesource.com/chromiumos/third_party/kernel into chromeos-3.8