xfs: merge xfs_ag.h into xfs_format.h

More on-disk format consolidation.  A few declarations that weren't on-disk
format related move into better suitable spots.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index b0447c8..d27804a 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -320,10 +320,7 @@
 
 /*
  * Per-ag incore structure, copies of information in agf and agi, to improve the
- * performance of allocation group selection. This is defined for the kernel
- * only, and hence is defined here instead of in xfs_ag.h. You need the struct
- * xfs_mount to be defined to look up a xfs_perag anyway (via mp->m_perag_tree),
- * so this doesn't introduce any strange header file dependencies.
+ * performance of allocation group selection.
  */
 typedef struct xfs_perag {
 	struct xfs_mount *pag_mount;	/* owner filesystem */