Merge changes from topic "bk/context_refactor" into integration

* changes:
  refactor(pmu): convert FEAT_MTPMU to C and move to persistent register init
  feat(pmu): introduce pmuv3 lib/extensions folder
  fix(pmu): make MDCR_EL3.MTPME=1 out of reset
  refactor(cm): introduce a real manage_extensions_nonsecure()