drm/i915/dg2: add DG2 platform info

DG2 has Xe_LPD display (version 13) and Xe_HPG (version 12.55) graphics.
There are two variants (treated as subplatforms in the code):  DG2-G10
and DG2-G11 that require independent programming in some areas (e.g.,
workarounds).

Bspec: 44472, 44474, 46197, 48028, 48077
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210721223043.834562-4-matthew.d.roper@intel.com