As during the plane cleanup, we wish to disable the hardware and
so may modify state on the associated CRTC, that CRTC must continue to
exist until we are finished.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=54101Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: stable@vger.kernel.org
Reviewed-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Nlu hua <huax.lu@intel.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>