Remove duplicates, add VLV specific macros for port B and C.

v2: also add PANEL_PORT_SELECT_DPC_VLV for clarity (Ville)
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Reviewed-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>