Merge changes from topic "mb/rst-to-bl31-update" into integration

* changes:
  docs: update RESET_TO_BL31 documentation
  fix(bl31): avoid clearing of argument registers in RESET_TO_BL31 case
  Revert "docs(bl31): aarch64: RESET_TO_BL31_WITH_PARAMS"
  Revert "feat(bl31): aarch64: RESET_TO_BL31_WITH_PARAMS"