CHROMIUM: drm/exynos: implement cursor ioctls.

The exynos display controllers (FIMD, MIXER) have special requirements
for scanning out small buffers. In particular, the ones used for cursors.

Implement the required padding in exynos drm driver so we can remove the
special cursor handling from DDX and just use cursor ioctls directly.

BUG=chromium:345164
TEST=cursor works on daisy. the following cases are tested:
  show/hide cursor
  changing cursor image (tested with webkit manual cursor test page)
  cursor at left/top/right/bottom edge of screen
  cursor on both internal panel and hdmi (move between two displays)
Signed-off-by: hshi@chromium.org

Change-Id: If71a8ef00f7901c30c7ac7ecba4ee9597792c838
Reviewed-on: https://chromium-review.googlesource.com/214074
Reviewed-by: Haixia Shi <hshi@chromium.org>
Tested-by: Haixia Shi <hshi@chromium.org>
Commit-Queue: Haixia Shi <hshi@chromium.org>
Merge branch 'chromeos-3.8' of https://chromium.googlesource.com/chromiumos/third_party/kernel into chromeos-3.8