drm/plane: add drmm_universal_plane_alloc()

Add an alternative to drm_universal_plane_init() that allocates
and initializes a plane and registers drm_plane_cleanup() with
drmm_add_action_or_reset().

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>