citra-qt: Add customizable speed limit target (#3353)

citra-qt: Add customizable speed limit target

* Update SDL config for the new frame_limit option
* Made max lag time a function of target speed percent.
* Added a checkbox to enable/disable frame limiter
* UI: Prevent frame_limit from under/overflowing
* UI: Hide target speed percent when frame limiter is off
* Disable frame limit spin box when framelimit isn't enabled

src/video_core/video_core.cpp

@@ -20,7 +20,6 @@ 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_vsync_enabled;
-std::atomic<bool> g_toggle_framelimit_enabled;
 
 /// Initialize the video core
 bool Init(EmuWindow* emu_window) {
@@ -47,4 +46,4 @@ void Shutdown() {
     LOG_DEBUG(Render, "shutdown OK");
 }
 
-} // namespace
+} // namespace VideoCore