Miscellaneous DSi NAND fixes (#1852)

* Replace some standard I/O calls with Platform equivalents

- I missed a spot when I submitted that PR a few months ago

* Include <memory> in DSi_NAND.h

- Because it uses unique_ptr

* Split DSi_NAND::ReadHardwareInfo into ReadSerialData and ReadHardwareInfoN

* Add a RegionMask enum

* Move DSi NAND patching to the frontend

* Add DSiSupportedLanguageMask

- Not currently used by the frontend, but I use it in melonDS DS

* Remove some Platform::ConfigEntry values

- The core no longer needs to know about them
- The corresponding Config values are unchanged

* Mark NANDMount's destructor as noexcept

src/Platform.h

@@ -121,13 +121,6 @@ enum ConfigEntry
     DSiSD_FolderSync,
     DSiSD_FolderPath,
 
-    Firm_OverrideSettings [[deprecated("Individual fields can now be overridden")]],
-    Firm_Username,
-    Firm_Language,
-    Firm_BirthdayMonth,
-    Firm_BirthdayDay,
-    Firm_Color,
-    Firm_Message,
     Firm_MAC,
 
     WifiSettingsPath,