Merge changes from topic "RDN2_WARM_REBOOT_WITH_SGI" into integration

Merge changes from topic "RDN2_WARM_REBOOT_WITH_SGI" into integration

* changes:
  feat(sgi): enable css implementation of warm reset
  feat(scmi): send powerdown request to online secondary cpus
  feat(plat/arm/css): add interrupt handler for reboot request
  refactor(psci): move psci_do_pwrdown_sequence() out of private header
  feat(plat/arm/css): add per-cpu power down support for warm reset
  feat(scmi): set warm reboot entry point
  fix(gicv3): update the affinity mask to 8 bit