Use config files to store whether SDMC is enabled or not, auto-create SDMC dir.

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).
Again, not sure what you mean by this. Can you give an example of what would be here? Like gamesaves, or something else that would go on the SD card?