GUI: Make multicore only work with Async and add GUI for multicore.

src/yuzu/main.h

@@ -235,6 +235,7 @@ private:
     QLabel* game_fps_label = nullptr;
     QLabel* emu_frametime_label = nullptr;
     QPushButton* async_status_button = nullptr;
+    QPushButton* multicore_status_button = nullptr;
     QPushButton* renderer_status_button = nullptr;
     QPushButton* dock_status_button = nullptr;
     QTimer status_bar_update_timer;