drm/nouveau/disp: Silence DCB warnings.

Most of these errors seem to be WFD related. Official documentation
says dcb type 8 is reserved. It's probably used for WFD. Silence
the warning in either case.

Connector type 70 is stated to be a virtual connector for WiFi
display. Since we know this, don't warn that we don't.

Signed-off by: Rosen Penev <rosenp@gmail.com>

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>