config: Add a setting for graphics V-Sync.

src/video_core/video_core.cpp

@@ -22,6 +22,7 @@ std::unique_ptr<RendererBase> g_renderer;             ///< Renderer plugin
 std::atomic<bool> g_hw_renderer_enabled;
 std::atomic<bool> g_shader_jit_enabled;
 std::atomic<bool> g_scaled_resolution_enabled;
+std::atomic<bool> g_vsync_enabled;
 
 /// Initialize the video core
 bool Init(EmuWindow* emu_window) {