refactor: report secondary EP register supported

Report `FFA_SECONDARY_EP_REGISTER_64` argument to `FFA_FEATURES`
supported when caller is SP with more than 1 vCPU.

Change-Id: If6247746d6f52c95e893d4978981693638897cf7
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/src/api.c b/src/api.c
index b519845..23af32e 100644
--- a/src/api.c
+++ b/src/api.c
@@ -2619,6 +2619,21 @@
 		}
 		return api_ffa_feature_success(0);
 
+	case FFA_SECONDARY_EP_REGISTER_64:
+		if (FFA_VERSION_COMPILED < FFA_VERSION_1_1) {
+			return ffa_error(FFA_NOT_SUPPORTED);
+		}
+
+		if (!(vm_id_is_current_world(current->vm->id) &&
+		      current->vm->vcpu_count > 1)) {
+			dlog_verbose(
+				"FFA_FEATURE: %s is only supported on SPs with "
+				"more than 1 vCPU\n",
+				ffa_func_name(function_or_feature_id));
+			return ffa_error(FFA_NOT_SUPPORTED);
+		}
+		return api_ffa_feature_success(0);
+
 	case FFA_RXTX_MAP_64: {
 		if (FFA_VERSION_1_2 > FFA_VERSION_COMPILED) {
 			return ffa_error(FFA_NOT_SUPPORTED);