drm/i915/gen9_bc: Introduce TGP PCH DDC pin mappings

With the introduction of gen9_bc, where Intel combines Cometlake CPUs with
a Tigerpoint PCH, we'll need to introduce new DDC pin mappings for this
platform in order to make all of the display connectors work. So, let's do
that.

Changes since v4:
* Split this into it's own patch - vsyrjala
Changes since v5:
* Rename gen9bc_port_to_ddc_pin() to gen9bc_tgp_port_to_ddc_pin()

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
[originally from Tejas's work]
Signed-off-by: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210209212832.1401815-3-lyude@redhat.com