turnip: improve perfetto sync_timestamp

tu_device_get_gpu_timestamp takes >100us on my otherwise idle sc7180.
Read the cpu block again after the call returns.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18238>

src/freedreno/vulkan/tu_perfetto.cc

@@ -194,6 +194,11 @@ sync_timestamp(struct tu_device *dev)
       return;
    }
 
+   /* get cpu timestamp again because tu_device_get_gpu_timestamp can take
+    * >100us
+    */
+   cpu_ts = perfetto::base::GetBootTimeNs().count();
+
    uint64_t current_suspend_count = 0;
    /* If we fail to get it we will use a fallback */
    tu_device_get_suspend_count(dev, &current_suspend_count);