xfs: add fs geometry bit for sparse inode chunks

Define an fs geometry bit for sparse inode chunks such that the
characteristic of the fs can be identified by userspace.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>