xfs: widen ondisk inode timestamps to deal with y2038+

xfs: widen ondisk inode timestamps to deal with y2038+

Source kernel commit: f93e5436f0ee5a85eaa3a86d2614d215873fb18b

Redesign the ondisk inode timestamps to be a simple unsigned 64-bit
counter of nanoseconds since 14 Dec 1901 (i.e. the minimum time in the
32-bit unix time epoch).  This enables us to handle dates up to 2486,
which solves the y2038 problem.

sandeen: update xfs_flags2diflags2() as well, to match

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>