Only ports B and C have the power sequencer and backlight controls,
so complain if we ever try to register an eDP connector on some other
port.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NImre Deak <imre.deak@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>