xfs: widen ondisk quota expiration timestamps to handle y2038+

Enable the bigtime feature for quota timers.  We decrease the accuracy
of the timers to ~4s in exchange for being able to set timers up to the
bigtime maximum.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>