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/config.cpp

@@ -55,9 +55,14 @@ void Config::ReadControls() {
     Settings::values.pad_sright_key = glfw_config->GetInteger("Controls", "pad_sright", GLFW_KEY_RIGHT);
 }
 
+void Config::ReadData() {
+    Settings::values.use_virtual_sd = glfw_config->GetBoolean("Data Storage", "use_virtual_sd", true);
+}
+
 void Config::Reload() {
     LoadINI(glfw_config, glfw_config_loc.c_str(), DefaultINI::glfw_config_file);
     ReadControls();
+    ReadData();
 }
 
 Config::~Config() {

src/citra/config.h

@@ -16,6 +16,7 @@ class Config {
 
     bool LoadINI(INIReader* config, const char* location, const std::string& default_contents="", bool retry=true);
     void ReadControls();
+    void ReadData();
 public:
     Config();
     ~Config();

src/citra/default_ini.h

@@ -25,6 +25,9 @@ pad_sup =
 pad_sdown =
 pad_sleft =
 pad_sright =
+
+[Data Storage]
+use_virtual_sd =
 )";
 
 }