drm/i915/dg2: add gsc with special gsc bar offsets

DG2 uses different GSC offsets on memory bar
and uses PXP head (HECI1).

v2 (Daniele): Rebased to before the ATS patches

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com> #v1
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220419193314.526966-7-daniele.ceraolospurio@intel.com