backend-drm: Don't try cursor buffers for client planes

For better or worse, cursor planes can only be used by uploaded SHM
buffers right now, so ignore them when we're calculating the acceptable
plane mask for client dmabufs.

Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/backend-drm/fb.c

@@ -581,6 +581,9 @@ drm_fb_get_from_view(struct drm_output_state *state, struct weston_view *ev,
 	/* Check if this buffer can ever go on any planes. If it can't, we have
 	 * no reason to ever have a drm_fb, so we fail it here. */
 	wl_list_for_each(plane, &b->plane_list, link) {
+		/* only SHM buffers can go into cursor planes */
+		if (plane->type == WDRM_PLANE_TYPE_CURSOR)
+			continue;
 		if (drm_fb_compatible_with_plane(fb, plane))
 			fb->plane_mask |= (1 << plane->plane_idx);
 	}