When everyone implements it exactly the same way, among all 4
implementations, there's not really a need to overwrite this at all.

Aside: drm_kms_helper_hotplug_event is pretty much core functionality
at this point. Probably should move it there.
Reviewed-by: Lyude Paul <lyude@redhat.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181128221234.15054-1-daniel.vetter@ffwll.ch