NFS: Clean up MNT program definitions

Clean up:  Relocate MNT program procedure number definitions to the
only file that uses them.  Relocate the version number definitions,
which are shared, to nfs.h.  Remove duplicate program number
definitions.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>