xfs: make struct xfs_perag kernel only

The struct xfs_perag has many kernel-only definitions in it,
requiring a __KERNEL__ guard so userspace can use it to. Move it to
xfs_mount.h so that it it kernel-only, and let userspace redefine
it's own version of the structure containing only what it needs.
This gets rid of another __KERNEL__ check in the XFS header files.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_symlink_remote.c b/fs/xfs/xfs_symlink_remote.c
index a318524..01c85e3 100644
--- a/fs/xfs/xfs_symlink_remote.c
+++ b/fs/xfs/xfs_symlink_remote.c
@@ -21,6 +21,7 @@
 #include "xfs_format.h"
 #include "xfs_log.h"
 #include "xfs_trans.h"
+#include "xfs_ag.h"
 #include "xfs_sb.h"
 #include "xfs_mount.h"
 #include "xfs_bmap_btree.h"