drm/i915: Move connector registration to driver registration

Defer connector registration from during construction to the driver
registration phase. This is important for ordering the action correctly,
e.g. not using debugfs before it is ready.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466773227-7994-4-git-send-email-chris@chris-wilson.co.uk