refactor(ff-a): direct messaging

Some functions from `src/ffa/{hypervisor,spmc}.c` were missed in the
refactoring.
Move them to `src/ffa/{hypervisor,spmc}/direct_messaging.c`.

Change-Id: Ic0a238fe676c8aa77110f539ccf9cdb9638b85e9
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/src/ffa/hypervisor/direct_messaging.c b/src/ffa/hypervisor/direct_messaging.c
index c5b5292..cfa663f 100644
--- a/src/ffa/hypervisor/direct_messaging.c
+++ b/src/ffa/hypervisor/direct_messaging.c
@@ -119,3 +119,17 @@
 	(void)current_locked;
 	(void)next_locked;
 }
+
+bool plat_ffa_handle_framework_msg(struct ffa_value args, struct ffa_value *ret)
+{
+	(void)args;
+	(void)ret;
+
+	return false;
+}
+
+bool plat_ffa_is_spmd_lp_id(ffa_id_t vm_id)
+{
+	(void)vm_id;
+	return false;
+}