[PATCH 0/2] fat: convert to the new mount API

[Eric Sandeen <sandeen@redhat.com>]

This short series converts the fat/vfat/msdos filesystem to use the
new mount API.

I've tested it with a hacky shell script found at 

https://gist.github.com/sandeen/3492a39c3f2bf16d1ccdd2cd1c681ccd

which tries every possible option, including some with invalid values,
on both vfat and msdos mounts. It then tests random combinations of
2, 3, and 4 options, including possibly invalid options.

I captured stdout from two runs with and without these modifications,
and the results are identical.

As patch 2 notes, I left codepage loading to fill_super(), rather than
validating codepage options as they are parsed. This is because i.e.

mount -o "iocharset=nope,iocharset=iso8859-1"

passes today, due to the last iocharset option being the only one that is
loaded. It might be nice to validate such options as they are parsed, but
doing so would make the above command line fail, so I'm not sure if it's
a good idea. I do have a patch to validate as we parse, if that's desired.

Lastly, this does not yet use the proposed uid/gid parsing helpers, since
that is not yet merged.

Thanks,
-Eric