drm/imx: don't wait for vblank and stop calling cleanup_planes in commit_tail

drm_atomic_helper_cleanup_planes only calls the cleanup_fb plane
helpers, which we don't implement as a CMA framebuffer based driver.
There is no reason to wait for vblanks in commit_tail only to do nothing
afterwards.

Signed-off-by: Philipp Zabel <[e-mail]>
Reviewed-by: Lucas Stach <[e-mail]>

drivers/gpu/drm/imx/imx-drm-core.c

···
 	drm_atomic_helper_commit_modeset_enables(dev, state);
 
 	drm_atomic_helper_commit_hw_done(state);
-
-	drm_atomic_helper_wait_for_vblanks(dev, state);
-
-	drm_atomic_helper_cleanup_planes(dev, state);
 }
 
 static const struct drm_mode_config_helper_funcs imx_drm_mode_config_helpers = {