Kconfig: Add Kconfig entry for Labeled NFS V4 client

This patch adds the NFS_V4_SECURITY_LABEL entry which
enables security label support for the NFSv4 client

Signed-off-by: Steve Dickson <steved@redhat.com>
[trond: Make this non-interactive]
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>