NFS: Use super.c for NFSROOT mount option parsing

Replace duplicate code in NFSROOT for mounting an NFS server on '/'
with logic that uses the existing mainline text-based logic in the NFS
client.

Add documenting comments where appropriate.

Note that this means NFSROOT mounts now use the same default settings
as v2/v3 mounts done via mount(2) from user space.

  vers=3,tcp,rsize=<negotiated default>,wsize=<negotiated default>

As before, however, no version/protocol negotiation with the server is
done.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 508f8cf..2a18f15 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -364,6 +364,7 @@
 extern void nfs_put_lock_context(struct nfs_lock_context *l_ctx);
 extern u64 nfs_compat_user_ino64(u64 fileid);
 extern void nfs_fattr_init(struct nfs_fattr *fattr);
+extern unsigned long nfs_inc_attr_generation_counter(void);
 
 extern struct nfs_fattr *nfs_alloc_fattr(void);
 
@@ -379,9 +380,12 @@
 	kfree(fh);
 }
 
+/*
+ * linux/fs/nfs/nfsroot.c
+ */
+extern int  nfs_root_data(char **root_device, char **root_data); /*__init*/
 /* linux/net/ipv4/ipconfig.c: trims ip addr off front of name, too. */
 extern __be32 root_nfs_parse_addr(char *name); /*__init*/
-extern unsigned long nfs_inc_attr_generation_counter(void);
 
 /*
  * linux/fs/nfs/file.c
@@ -584,10 +588,6 @@
 	return ino;
 }
 
-/* NFS root */
-
-extern void * nfs_root_data(void);
-
 #define nfs_wait_event(clnt, wq, condition)				\
 ({									\
 	int __retval = wait_event_killable(wq, condition);		\