drm/i915: Set aux.dev to the drm_connector device, instead of drm_device.

So far, the i915 driver and some other drivers set it to the drm_device,
which doesn't allow one to know which DP a given aux channel is related
to. Changing this to be the drm_connector provides proper nesting, still
allowing one to get the drm_device from it. Some drivers already set it
to the drm_connector.

This also removes the need to add a sysfs link for the i2c device under
the connector, as it will already be there.

v9:
 - As a side effect, drm_dp_aux_unregister() must be called before
 intel_connector_unregister(), as both the aux.dev and the i2c adapter
 dev are children of the drm_connector device now. Calling
 drm_dp_aux_unregister() before prevents them from being destroyed
 twice.

v10:
 - move aux_fini() to connector_unregister(), instead of moving
 drm_dp_aux_unregister() outside of connector_register().

Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1453417821-2811-4-git-send-email-rafael.antognolli@intel.com