drm/nouveau/kms/gv100-: Add support for interlaced modes

We advertise being able to set interlaced modes, so let's actually make
sure to do that. Otherwise, we'll end up hanging the display engine due
to trying to set a mode with timings adjusted for interlacing without
telling the hardware it's actually an interlaced mode.

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