[GFS2] Move glock hash table out of superblock

There are several reasons why we want to do this:
 - Firstly its large and thus we'll scale better with multiple
   GFS2 fs mounted at the same time
 - Secondly its easier to scale its size as required (thats a plan
   for later patches)
 - Thirdly, we can use kzalloc rather than vmalloc when allocating
   the superblock (its now only 4888 bytes)
 - Fourth its all part of my plan to eventually be able to use RCU
   with the glock hash.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/glock.h

@@ -150,4 +150,6 @@ void gfs2_reclaim_glock(struct gfs2_sbd *sdp);
 void gfs2_scand_internal(struct gfs2_sbd *sdp);
 void gfs2_gl_hash_clear(struct gfs2_sbd *sdp, int wait);
 
+int __init gfs2_glock_init(void);
+
 #endif /* __GLOCK_DOT_H__ */