feat(spmc): add support for direct req/resp

Enable the SPMC to handle FFA_MSG_SEND_DIRECT_REQ and
FFA_MSG_SEND_DIRECT_RESP ABIs.

Signed-off-by: Marc Bonnici <marc.bonnici@arm.com>
Change-Id: Ia196c7405993f600e4fdbf467397ea3fb035a62a
1 file changed