drm-backend: fix deinit_planes

Commit "drm-backend: move code to init/deinit planes to specific
functions" lost a chunk of drm_output_deinit() when moving code into
drm_output_deinit_planes(). Reinstate the missing chunk.

This fixes an endless loop over weston_compositor::plane_list when you
start with three monitors connected, unplug and re-plug one.

Fixes: 3be23eff99

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/backend-drm/drm.c

@@ -1706,6 +1706,16 @@ drm_output_deinit_planes(struct drm_output *output)
 	/* If the compositor is already shutting down, the planes have already
 	 * been destroyed. */
 	if (!b->shutting_down) {
+		wl_list_remove(&output->scanout_plane->base.link);
+		wl_list_init(&output->scanout_plane->base.link);
+
+		if (output->cursor_plane) {
+			wl_list_remove(&output->cursor_plane->base.link);
+			wl_list_init(&output->cursor_plane->base.link);
+			/* Turn off hardware cursor */
+			drmModeSetCursor(b->drm.fd, output->crtc->crtc_id, 0, 0, 0);
+		}
+
 		if (!b->universal_planes) {
 			/* Without universal planes, our special planes are
 			 * pseudo-planes allocated at output creation, freed at