mkfs: Introduce mkfs configuration structure

mkfs: Introduce mkfs configuration structure

Formatting the on disk XFS structures requires a certain set of
validated and calculated parameters. By the time we start writing
information to disk this has all been done. Abstract this information
out into a separate structures and initialise it with all the
calculated parameters so we can factor the mkfs formatting code
to use it.

Signed-Off-By: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>