drm/vc4: Use drm_atomic_helper_shutdown

drm_plane_helper_disable is a non-atomic drivers only function, and
will blow up (since no one passes the locking context it needs).

Atomic drivers which want to quiescent their hw on unload should
use drm_atomic_helper_shutdown() instead.

v2: Rebase.

Reviewed-by: Ville Syrjälä <[e-mail]>
Acked-by: Eric Anholt <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Cc: Eric Anholt <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/vc4/vc4_drv.c

···
 #include <linux/pm_runtime.h>
 #include <drm/drm_fb_cma_helper.h>
 #include <drm/drm_fb_helper.h>
+#include <drm/drm_atomic_helper.h>
 
 #include "uapi/drm/vc4_drm.h"
 #include "vc4_drv.h"
···
 	struct vc4_dev *vc4 = to_vc4_dev(drm);
 
 	drm_dev_unregister(drm);
+
+	drm_atomic_helper_shutdown(drm);
 
 	drm_mode_config_cleanup(drm);
 

drivers/gpu/drm/vc4/vc4_plane.c

···
 
 static void vc4_plane_destroy(struct drm_plane *plane)
 {
-	drm_plane_helper_disable(plane, NULL);
 	drm_plane_cleanup(plane);
 }