Test, fix and re-enable non-FAT32 filesystem support

[InvoxiPlayGames]

Make sure kboot.conf, Linux and libxenon homebrew can be booted still from mediums other than a FAT32 USB.

Current status:

• ISO9660 (CD/DVD)
• FATX
• ext2 (low-prio)

[IAmNadaman]

I believe these features have to be added back into LibXenon in order to function in XeLL, yes?