drm/i915/chv: Try to program the PHY used clock channel overrides

These should make it possible to feed port C from pipe A or port B from
pipe B. Didn't quite seem to work though.

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>