xfs: move acl structures to xfs_format.h

Move the on-disk ACL format to xfs_format.h, so that repair can
use the common defintion.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>