drm/i915/chv: Fix PORT_TO_PIPE for CHV

Fix the encoder .get_config hooks to report the correct active pipe for
CHV.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Antti Koskipää <antti.koskipaa@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>