drm/i915/rkl: Add DDC pin mapping

The pin mapping for the final two outputs varies according to which PCH
is present on the platform:  with TGP the pins are remapped into the TC
range, whereas with CMP they stay in the traditional combo output range.

Bspec: 49181
Cc: Aditya Swarup <aditya.swarup@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200603211529.3005059-9-matthew.d.roper@intel.com