Merge changes from topic "ffa_el3_spmc" into integration

* changes:
  feat(spmc): enable the SPMC to pass the linear core ID in a register
  feat(spmc): add FFA_RX_RELEASE handler
  feat(spmc): add FFA_RUN handler
  feat(spmc): support FFA_ID_GET ABI
  feat(spmc): add FFA_FEATURES handler
  feat(spmc): add FFA_PARTITION_INFO_GET handler
  feat(spmc): enable handling FF-A RX/TX Mapping ABIs
  docs(maintainers): introduce SPMC maintainer section