Compatibility with M.2 Loader

[webhdx]

When M.2 Loader is out, PicoBoot needs to be ready to boot from it day 1. This requires updating iplboot with M.2 Loader protocol support. This isn't too difficult as the communication is already implemented into Swiss. This code then has to be integrated with FatFS library by writing glue functions.

In my opinion M.2 Loader should have higher priority than SD cards in the boot chain but this has to be discussed with iplboot maintainer. Alternatively booting from M.2 Loader could be implemented into PicoBoot's bootloader (#61).