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 --cc fs/xfs/xfs_acl.c
Simple merge

diff --cc fs/xfs/xfs_ag.h
Simple merge

diff --cc fs/xfs/xfs_mount.h
Simple merge

diff --cc fs/xfs/xfs_symlink_remote.c
Simple merge