[SPM] tidying common code to tftf and cactus

This patch moves the code used to test SPM functionality, not explicitly
described in FF-A specification, from ffa_helpers to spm_common which is
built for both tftf and cactus.

Signed-off-by: Max Shvetsov <maksims.svecovs@arm.com>
Change-Id: I461efad977cc4d02701feea7b2215a61453716ef
diff --git a/spm/cactus/cactus_tests.h b/spm/cactus/cactus_tests.h
index fd229bf..8e838cc 100644
--- a/spm/cactus/cactus_tests.h
+++ b/spm/cactus/cactus_tests.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017-2020, Arm Limited. All rights reserved.
+ * Copyright (c) 2017-2021, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -7,7 +7,7 @@
 #ifndef CACTUS_TESTS_H
 #define CACTUS_TESTS_H
 
-#include <ffa_helpers.h>
+#include <spm_common.h>
 
 /*
  * Test functions