xfs: convert inode shrinker to per-filesystem contexts

Now the shrinker passes us a context, wire up a shrinker context per
filesystem. This allows us to remove the global mount list and the
locking problems that introduced. It also means that a shrinker call
does not need to traverse clean filesystems before finding a
filesystem with reclaimable inodes.  This significantly reduces
scanning overhead when lots of filesystems are present.

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

diff --cc fs/xfs/linux-2.6/xfs_super.c
Simple merge

diff --cc fs/xfs/linux-2.6/xfs_sync.c
Simple merge

diff --cc fs/xfs/linux-2.6/xfs_sync.h
Simple merge

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