drm/i915/tgl: Add TGL PCH detection in virtualized environment

Assume PCH_TGP when platform is TGL.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190711173115.28296-5-lucas.demarchi@intel.com