Pull in the drm vblank rework from Ville and me. drm core parts acked
by Dave Airlie

Conflicts:
	drivers/gpu/drm/i915/intel_display.c

Just a bit of fun around the placement of drm_vblank_on. This merge
resolution has been tested in drm-intel-nightly for a while already.
Acked-by: NDave Airlie <airlied@gmail.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>