linux-wandboard

drm/i915: fully switch off overlay when not in use

Now that the cache flushing of the memory based overlay regs works,
we can safely switch off the overlay. Beforehand it was only disabled
(like in userspace).

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Eric Anholt <eric@anholt.net>