drm/i915/tgl: apply Display WA #1178 to fix type C dongles

Add port C to workaround to cover Tiger Lake.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190708231629.9296-22-lucas.demarchi@intel.com
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190711213517.13674-1-lucas.demarchi@intel.com