drm/i915/gen9_bc: Recognize TGP PCH + CML combos

Since Intel has introduced the gen9_bc platform, a combination of
Tigerpoint PCHs and CML CPUs, let's recognize such platforms as valid and
avoid WARNing on them.

Changes since v4:
* Split this into it's own patch - vsyrjala

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/20210209212832.1401815-2-lyude@redhat.com