nfsd41: xdr infrastructure

Define nfsd41_dec_ops vector and add it to nfsd4_minorversion for
minorversion 1.

Note: nfsd4_enc_ops vector is shared for v4.0 and v4.1
since we don't need to filter out obsolete ops as this is
done in the decoding phase.

exchange_id, create_session, destroy_session, and sequence ops are
implemented as stubs returning nfserr_opnotsupp at this stage.

[was nfsd41: xdr stubs]
[get rid of CONFIG_NFSD_V4_1]
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>