xfs: integrate xfs_quota_priv header file to xfs_qm

The xfs_quota_priv header file is only included by xfs_qm header and
there is no much users for its contents, hence we can move those stuff
to xfs_qm header file and kill it.

This patch also remove an unused macro DQFLAGTO_TYPESTR.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>