Test: Add Secure SFN Backend test

This patch adds Secure SFN Backend test (PSA API tests):
- Adding a new TEST_S_SFN_BACKEND_TEST config and enable by default
  for TEST_S
- Adding Secure test source and CMakeLists

Change-Id: Ife229c2c7c5abbf84effc18b0951f6a4eb5acace
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
diff --git a/test/secure_fw/secure_suites.c b/test/secure_fw/secure_suites.c
index 674144e..3d7536b 100644
--- a/test/secure_fw/secure_suites.c
+++ b/test/secure_fw/secure_suites.c
@@ -28,13 +28,15 @@
 #ifdef TEST_S_PLATFORM
 #include "platform_s_tests.h"
 #endif
-#ifdef TEST_S_IPC
-#include "ipc_s_tests.h"
-#else
 #ifdef TEST_S_AUDIT
 #include "audit_s_tests.h"
 #endif
-#endif /* TFM_PSA_API */
+#ifdef TEST_S_IPC
+#include "ipc_s_tests.h"
+#endif
+#ifdef TEST_S_SFN_BACKEND
+#include "sfn_s_tests.h"
+#endif
 #if defined (TEST_S_FPU)
 #include "fpu_s_tests.h"
 #endif
@@ -88,6 +90,11 @@
     {&register_testsuite_s_ipc_interface, 0, 0, 0},
 #endif
 
+#ifdef TEST_S_SFN_BACKEND
+    /* Secure SFN backend test cases */
+    {&register_testsuite_s_sfn_interface, 0, 0, 0},
+#endif
+
 #ifdef TEST_S_FPU
     /* Secure FPU test cases */
     {&register_testsuite_s_fpu_interface, 0, 0, 0},