backend/drm: Destroy page flips on backend destroy

When we destroy the backend, page flips will no longer be invoked meaning
those won't clean up the page flips for us.

backend/drm/backend.c

@@ -39,6 +39,11 @@ static void backend_destroy(struct wlr_backend *backend) {
 		destroy_drm_connector(conn);
 	}
 
+	struct wlr_drm_page_flip *page_flip, *page_flip_tmp;
+	wl_list_for_each_safe(page_flip, page_flip_tmp, &drm->page_flips, link) {
+		drm_page_flip_destroy(page_flip);
+	}
+
 	wlr_backend_finish(backend);
 
 	wl_list_remove(&drm->display_destroy.link);

backend/drm/drm.c

@@ -420,7 +420,7 @@ static void drm_connector_set_pending_page_flip(struct wlr_drm_connector *conn,
 	conn->pending_page_flip = page_flip;
 }
 
-static void page_flip_destroy(struct wlr_drm_page_flip *page_flip) {
+void drm_page_flip_destroy(struct wlr_drm_page_flip *page_flip) {
 	if (!page_flip) {
 		return;
 	}
@@ -476,7 +476,7 @@ static bool drm_crtc_commit(struct wlr_drm_connector *conn,
 			drm_fb_clear(&layer->pending_fb);
 		}
 
-		page_flip_destroy(page_flip);
+		drm_page_flip_destroy(page_flip);
 	}
 	return ok;
 }
@@ -1696,7 +1696,7 @@ static void handle_page_flip(int fd, unsigned seq,
 	if (conn != NULL) {
 		conn->pending_page_flip = NULL;
 	}
-	page_flip_destroy(page_flip);
+	drm_page_flip_destroy(page_flip);
 
 	if (conn == NULL) {
 		return;

include/backend/drm/drm.h

@@ -193,6 +193,7 @@ bool drm_connector_supports_vrr(struct wlr_drm_connector *conn);
 size_t drm_crtc_get_gamma_lut_size(struct wlr_drm_backend *drm,
 	struct wlr_drm_crtc *crtc);
 void drm_lease_destroy(struct wlr_drm_lease *lease);
+void drm_page_flip_destroy(struct wlr_drm_page_flip *page_flip);
 
 struct wlr_drm_fb *get_next_cursor_fb(struct wlr_drm_connector *conn);
 struct wlr_drm_layer *get_drm_layer(struct wlr_drm_backend *drm,