Add option to configure to download system files from Nintendo Update Service (#6269)

Co-authored-by: B3n30 <benediktthomas@gmail.com>

src/citra_qt/configuration/configure_system.h

@@ -43,6 +43,8 @@ private:
 
     void SetupPerGameUI();
 
+    void DownloadFromNUS();
+
     ConfigurationShared::CheckState is_new_3ds;
     std::unique_ptr<Ui::ConfigureSystem> ui;
     bool enabled = false;