xfs: remove direct calls to _qm_dqread

The quota initialization code needs an "uncached" variant of _dqget to
read in default quota limits and timers before the dquot cache is fully
set up.  We've already split up _dqget into its component pieces so
create a fourth variant to address this need, and make dqread internal
to xfs_dquot.c again.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>