NFSv4: Prepare for minorversion-specific nfs_server capabilities

Clean up the setting of the nfs_server->caps, by shoving it all
into nfs4_server_common_setup().
Then add an 'initial capabilities' field into struct nfs4_minor_version_ops.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>