vhost-user-gpu: skip VHOST_USER_GPU_UPDATE when !PIXMAN

This simply means that 2d drawing updates won't be handled, but 3d
should work.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>

hw/display/vhost-user-gpu.c

@@ -307,6 +307,7 @@ vhost_user_gpu_handle_display(VhostUserGPU *g, VhostUserGpuMsg *msg)
         dpy_gl_update(con, m->x, m->y, m->width, m->height);
         break;
     }
+#ifdef CONFIG_PIXMAN
     case VHOST_USER_GPU_UPDATE: {
         VhostUserGpuUpdate *m = &msg->payload.update;
 
@@ -334,6 +335,7 @@ vhost_user_gpu_handle_display(VhostUserGPU *g, VhostUserGpuMsg *msg)
         }
         break;
     }
+#endif
     default:
         g_warning("unhandled message %d %d", msg->request, msg->size);
     }