drm/nouveau/kms/nv50-: Probe SOR and PIOR caps for DP interlacing support

Right now, we make the mistake of allowing interlacing on all
connectors. Nvidia hardware does not always support interlacing with DP
though, so we need to make sure that we don't allow interlaced modes to
be set in such situations as otherwise we'll end up accidentally hanging
the display HW.

This fixes some hangs with Turing, which would be caused by attempting
to set an interlaced mode on hardware that doesn't support it. This
patch likely fixes other hardware hanging in the same way as well.

Note that we say we probe PIOR caps, but they don't actually have any
interlacing caps. So, the get_caps() function for PIORs just sets
interlacing support to true.

Changes since v1:
* Actually probe caps correctly this time, both on EVO and NVDisplay.
Changes since v2:
* Fix probing for < GF119
* Use vfunc table, in prep for adding more caps in the future.

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