test(ff-a): check w3 for ffa_partition_info_get

Check that the size of the partition info descriptor is correctly
populated when calling ffa_partition_info_get.

Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
Change-Id: I56fa0e82e52c1ed35fc2ea0208d69eabc5800935
diff --git a/include/runtime_services/ffa_helpers.h b/include/runtime_services/ffa_helpers.h
index 1250673..0ad8c42 100644
--- a/include/runtime_services/ffa_helpers.h
+++ b/include/runtime_services/ffa_helpers.h
@@ -220,6 +220,11 @@
 	return (uint32_t)val.arg2;
 }
 
+static inline uint32_t ffa_partition_info_desc_size(struct ffa_value val)
+{
+	return (uint32_t)val.arg3;
+}
+
 static inline uint32_t ffa_feature_intid(struct ffa_value val)
 {
 	return (uint32_t)val.arg2;