Driver camera view when in reverse

Added toggle to show the driver camera when in the reverse gear.

selfdrive/ui/qt/widgets/cameraview.cc

@@ -217,6 +217,9 @@ void CameraWidget::updateFrameMat() {
     if (active_stream_type == VISION_STREAM_DRIVER) {
       if (stream_width > 0 && stream_height > 0) {
         frame_mat = get_driver_view_transform(w, h, stream_width, stream_height);
+        if (uiState()->scene.show_driver_camera) {
+          frame_mat.v[0] *= -1.0;
+        }
       }
     } else {
       // Project point at "infinity" to compute x and y offsets