drm/nouveau/device: pass instance id when looking up a subdev/engine

This switches to using the subdev list for lookup, and otherwise should
be a no-op aside from switching the function signatures.

Callers will be transitioned to split type+inst individually.

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