backend/drm: fix timeline feature flag on multi-GPU setups

This piece of code checks for multi-GPU renderer support, so it
needs to run after the renderer is initialized.

Fixes: 514c4b4cce01 ("backend: add timeline feature flag")
Closes: https://github.com/swaywm/sway/issues/8382

backend/drm/backend.c

@@ -264,6 +264,12 @@ struct wlr_backend *wlr_drm_backend_create(struct wlr_session *session,
 		}
 	}
 
+	drm->backend.features.timeline = drm->iface != &legacy_iface;
+	if (drm->parent) {
+		drm->backend.features.timeline = drm->backend.features.timeline &&
+			drm->mgpu_renderer.wlr_rend->features.timeline;
+	}
+
 	drm->session_destroy.notify = handle_session_destroy;
 	wl_signal_add(&session->events.destroy, &drm->session_destroy);
 

backend/drm/drm.c

@@ -126,12 +126,6 @@ bool check_drm_features(struct wlr_drm_backend *drm) {
 		drm->supports_tearing_page_flips = drmGetCap(drm->fd, DRM_CAP_ATOMIC_ASYNC_PAGE_FLIP, &cap) == 0 && cap == 1;
 	}
 
-	drm->backend.features.timeline = drm->iface != &legacy_iface;
-	if (drm->parent) {
-		drm->backend.features.timeline = drm->backend.features.timeline &&
-			drm->mgpu_renderer.wlr_rend->features.timeline;
-	}
-
 	if (env_parse_bool("WLR_DRM_NO_MODIFIERS")) {
 		wlr_log(WLR_DEBUG, "WLR_DRM_NO_MODIFIERS set, disabling modifiers");
 	} else {