[GFS2] Export lm_interface to kernel headers

lm_interface.h has a few out of the tree clients such as GFS1
and userland tools.

Right now, these clients keeps a copy of the file in their build tree
that can go out of sync.

Move lm_interface.h to include/linux, export it to userland and
clean up fs/gfs2 to use the new location.

Signed-off-by: Fabio M. Di Nitto <fabbione@ubuntu.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/ops_vm.c

@@ -15,9 +15,9 @@
 #include <linux/mm.h>
 #include <linux/pagemap.h>
 #include <linux/gfs2_ondisk.h>
+#include <linux/lm_interface.h>
 
 #include "gfs2.h"
-#include "lm_interface.h"
 #include "incore.h"
 #include "bmap.h"
 #include "glock.h"