We added crtc_id to the atomic ioctl, but forgot to add it for vblank
and page flip events. Commit bd386e518056 ("drm: Reorganize
drm_pending_event to support future event types [v2]") added it to
the vblank event, but page flip event was still missing.
Correct this and add a test for making sure we always set crtc_id correctly.