Merge branch 'topic/xehp-dg2-definitions-2021-07-21' into drm-intel-gt-next

As we begin applying XeHP and DG2 patches, the basic platform
definitions and macros (like IS_DG2()) will be needed in both
drm-intel-next and drm-intel-gt-next.  Those initial definition patches
are applied to a topic branch and merged to both trees.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>