drm/nouveau/disp: introduce acquire/release display path methods

These exist to give NVKM information on the set of display paths that
the DD needs to be active at any given time.

Previously, the supervisor attempted to determine this solely from OR
state, but there's a few configurations where this information on its
own isn't enough to determine the specific display paths in question:

- ANX9805, where the PIOR protocol for both DP and TMDS is TMDS.
- On a device using DCB Switched Outputs.
- On GM20x and newer, with a crossbar between the SOR and macro links.

After this commit, the DD tells NVKM *exactly* which display path it's
attempting a modeset on.

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