drm: Automatically register/unregister all connectors

As the drm_connector is now safe for multiple calls to
register/unregister, automatically perform a registration on all known
connectors drm drv_register (and unregister from drm_drv_unregister).
Drivers can still call drm_connector_register() and
drm_connector_unregister() individually, or defer as required.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1466151923-1572-2-git-send-email-chris@chris-wilson.co.uk