Add some definitions for NFSv4.2 which will be used by subsequent commits.

This is a preliminary commit of NFSv4.2 definitions that will be used by
subsequent commits which adds NFSv4.2 support to the NFS client and server.

There will be a series of these preliminary commits that will prepare for
a major commit of the NFSv4.2 client/server changes currently found in
subversion under projects/nfsv42/sys.