Test: Create SST test service

This patch adds a new secure service for use by
the SST test suites. The initial implementation
enables testing of the SST access by reference
feature.

Change-Id: I41663255bd65aa72168ba6d32c47b23e65586001
Signed-off-by: Jamie Fox <jamie.fox@arm.com>
diff --git a/interface/include/tfm_ns_svc.h b/interface/include/tfm_ns_svc.h
index e83b076..75b78ec 100644
--- a/interface/include/tfm_ns_svc.h
+++ b/interface/include/tfm_ns_svc.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, Arm Limited. All rights reserved.
+ * Copyright (c) 2017-2018, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  *
@@ -47,6 +47,13 @@
     SVC_TFM_CORE_TEST_MULTIPLE_CALLS,
 #endif /* CORE_TEST_SERVICES */
 
+#if defined(SST_TEST_SERVICES)
+    SVC_SST_TEST_SERVICE_SETUP,
+    SVC_SST_TEST_SERVICE_DUMMY_ENCRYPT,
+    SVC_SST_TEST_SERVICE_DUMMY_DECRYPT,
+    SVC_SST_TEST_SERVICE_CLEAN,
+#endif /* SST_TEST_SERVICES */
+
     /* add all the new entries above this line */
     SVC_TFM_MAX,
 };