intel/genxml: add generic perf counters registers

intel/genxml: add generic perf counters registers

We have 2 of those we can configure to source programmable events.
Those are not part of the OA reports. Configuration happens in i915
through the metric set selected by the application. On the Mesa side
we'll just sample those and do a diff.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>