Use QPixmap/QIcon for background color selection button

src/yuzu/configuration/configure_graphics.h

@@ -23,6 +23,8 @@ public:
 private:
     void setConfiguration();
 
+    void UpdateBackgroundColorButton(QColor color);
+
     std::unique_ptr<Ui::ConfigureGraphics> ui;
     QColor bg_color;
 };