drm/i915/pmu: Support PMU for all engines

Given how the metrics are already exported, we also need to run sampling
over engines from all GTs.

Problem of GT frequencies is left for later.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230519154946.3751971-3-umesh.nerlige.ramappa@intel.com