VFS: Unexport do_kern_mount() and clean up simple_pin_fs()

Replace all module uses with the new vfs_kern_mount() interface, and fix up
simple_pin_fs().

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/Documentation/filesystems/automount-support.txt b/Documentation/filesystems/automount-support.txt
index 58c65a1..7cac200 100644
--- a/Documentation/filesystems/automount-support.txt
+++ b/Documentation/filesystems/automount-support.txt
@@ -19,7 +19,7 @@
 
  (2) Have the follow_link() op do the following steps:
 
-     (a) Call do_kern_mount() to call the appropriate filesystem to set up a
+     (a) Call vfs_kern_mount() to call the appropriate filesystem to set up a
          superblock and gain a vfsmount structure representing it.
 
      (b) Copy the nameidata provided as an argument and substitute the dentry