drm/nouveau/kms/gv100-: avoid sending a core update until the first modeset

drm/nouveau/kms/gv100-: avoid sending a core update until the first modeset

The OR routing logic in NVKM does not expect to receive supervisor
interrupts until the DD has provided consistent information on the
ORs it's using and the EVO/NVD assembly state to match.

The combination of changing window ownership + core channel update
during display init triggered a situation where we'd disconnect an
OR from the pad it was meant to still be driving on some systems.

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