Use config files to store whether SDMC is enabled or not

Before, it used to use whether the directory actually existed. As a result, .citra-emu/sdmc was never auto-created (something quite confusing to me until I read through the logs).

src/citra_qt/config.cpp

@@ -64,12 +64,26 @@ void Config::SaveControls() {
     qt_config->endGroup();
 }
 
+void Config::ReadData() {
+    qt_config->beginGroup("Data Storage");
+    Settings::values.use_virtual_sd = qt_config->value("use_virtual_sd", true).toBool();
+    qt_config->endGroup();
+}
+
+void Config::SaveData() {
+    qt_config->beginGroup("Data Storage");
+    qt_config->setValue("use_virtual_sd", Settings::values.use_virtual_sd);
+    qt_config->endGroup();
+}
+
 void Config::Reload() {
     ReadControls();
+    ReadData();
 }
 
 void Config::Save() {
     SaveControls();
+    SaveData();
 }
 
 Config::~Config() {

src/citra_qt/config.h

@@ -14,6 +14,9 @@ class Config {
 
     void ReadControls();
     void SaveControls();
+
+    void ReadData();
+    void SaveData();
 public:
     Config();
     ~Config();