Merge changes from topic "ffa_el3_spmc" into integration

* changes:
  feat(spmc): add support for direct req/resp
  feat(spmc): add support for handling FFA_ERROR ABI
  feat(spmc): add support for FFA_MSG_WAIT
  feat(spmc): add function to determine the return path from the SPMC
  feat(spmd): enable handling of FF-A SMCs with the SPMC at EL3
  feat(spmd): update SPMC init flow to use EL3 implementation
  feat(spmc): add FF-A secure partition manager core
  feat(spmc): prevent read only xlat tables with the EL3 SPMC
  feat(spmc): enable building of the SPMC at EL3
  refactor(spm_mm): reorganize secure partition manager code