CFG:U: Implemented the GetCountryCodeID and GetCountryCodeString

I couldn't find a way to retrieve all the country code strings, and the ones in there need to be checked, probably using a real 3DS.
Does the 3DS send those strings with a NULL terminator? that's another thing that has to be checked on a real 3DS.
Document the known inputs and outputs of these functions (from 3dbrew or whatever, even if you don't necessarily implement functionality for all of them) in a docstring. We've been using a common format, e.g. https://github.com/citra-emu/citra/blob/master/src/core/hle/service/fs_user.cpp#L75