drm/i915/chv: Reset data lanes in encoder .post_disable() hook

Seems like we shouldn't leave the data lane resert deasserted when
the port if disabled. So propagate the reset the data lanes in
the encoder .post_disable() hook.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>