lib/i915: prepare codegen for new ACM/DG2 variables

v2:
- Patches are being merged as a split series, so drop the new OA format
  from this series and introduce it in the second part of the series.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>