nfs_common: make include/linux/nfs4.h include generated nfs4_1.h

In the long run, the NFS development community intends to autogenerate a
lot of the XDR handling code.  Both the NFS client and server include
"include/linux/nfs4.hi". That file was hand-rolled, and some of the symbols
in it conflict with the autogenerated symbols.

Add a small nfs4_1.x to Documentation that currently just has the
necessary definitions for the delstid draft, and generate the relevant
header and source files. Make include/linux/nfs4.h include the generated
include/linux/sunrpc/xdrgen/nfs4_1.h and remove the conflicting
definitions from it and nfs_xdr.h.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>