feat(indirect message): forward FFA_RX_RELEASE to SPMC

Within FF-A v1.1 indirect messaging, the SPMC owns a VM's RX buffers;
the Hypervisor must acquire ownership through FFA_RX_ACQUIRE ABI when
it needs to deliver a message to a VM, and notify the SPMC when the VM
releases it, by forwarding FFA_RX_RELEASE messages.

SPMC's view of a VM mailbox may not follow current mailbox
FSM (empty->received->read->empty), SPMC may not be aware of VM
message delivery and the consequent received->read mailbox transition.

Change-Id: I391054410573cc80549905f1a4bd2bbd19ac17fe
Signed-off-by: Federico Recanati <federico.recanati@arm.com>
diff --git a/src/arch/fake/hypervisor/ffa.c b/src/arch/fake/hypervisor/ffa.c
index 2537dc0..252d174 100644
--- a/src/arch/fake/hypervisor/ffa.c
+++ b/src/arch/fake/hypervisor/ffa.c
@@ -99,6 +99,22 @@
 	return false;
 }
 
+bool plat_ffa_rx_release_forward(struct vm_locked vm_locked,
+				 struct ffa_value *ret)
+{
+	(void)vm_locked;
+	(void)ret;
+
+	return false;
+}
+
+bool plat_ffa_rx_release_forwarded(struct vm_locked vm_locked)
+{
+	(void)vm_locked;
+
+	return false;
+}
+
 bool plat_ffa_acquire_receiver_rx(struct vm_locked to_locked,
 				  struct ffa_value *ret)
 {