refactor(ff-a): split `sender_receiver` field

Split `sender_receiver` field into separate `sender` and `receiver`
fields so the compiler will do the shifts and masks for us.

Change-Id: I94a16c5e54779335f39579428dd37385590f7cf0
Signed-off-by: Karl Meakin <karl.meakin@arm.com>
diff --git a/test/hftest/service_common.c b/test/hftest/service_common.c
index 6ff2c71..6ac9162 100644
--- a/test/hftest/service_common.c
+++ b/test/hftest/service_common.c
@@ -349,7 +349,7 @@
 	bitmap = ffa_notification_get_from_framework(ret);
 	ASSERT_TRUE(is_ffa_spm_buffer_full_notification(bitmap) ||
 		    is_ffa_hyp_buffer_full_notification(bitmap));
-	ASSERT_EQ(own_id, ffa_rxtx_header_receiver(&message->header));
+	ASSERT_EQ(own_id, message->header.receiver);
 
 	if (ctx->is_ffa_manifest_parsed &&
 	    ctx->partition_manifest.run_time_el == S_EL1) {