xfs: cleanup uuid handling

The uuid table handling should not be part of a semi-generic uuid library
but in the XFS code using it, so move those bits to xfs_mount.c and
refactor the whole glob to make it a proper abstraction.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Felix Blyakher <felixb@sgi.com>