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/default_ini.h

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