drm/i915: Move intel_connector->unregister to connector->early_unregister

We now have a connector->func that serves the same purpose as our own
intel_connector->unregister vfunc allowing us to unwrap ourselves and
use drm_connector_register() (and friends) as the central function.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466160034-12173-2-git-send-email-chris@chris-wilson.co.uk