nouveau/gsp: add three notifier callbacks that we see in normal operation (v2)

Add NULL callbacks for some things GSP calls that we don't handle, but know about
so we avoid the logging.

v2: Timur suggested allowing null fn.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222043308.3090089-2-airlied@gmail.com