ITS: Implement the top layer of the ITS service

Implements the secure and non-secure top layer of the ITS service,
including a new manifest file, and generates the required veneers.
Updates the partition manifest with added SIDs. It also adds the
necessary CMake files to build the ITS service.

Change-Id: I6d66b01de56145d24a0bcbf0597ca158b6da3386
Signed-off-by: Tudor Cretu <tudor.cretu@arm.com>
diff --git a/interface/include/tfm_its_defs.h b/interface/include/tfm_its_defs.h
new file mode 100644
index 0000000..852f8f4
--- /dev/null
+++ b/interface/include/tfm_its_defs.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2019, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ */
+
+#ifndef __TFM_ITS_DEFS_H__
+#define __TFM_ITS_DEFS_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Invalid UID */
+#define TFM_ITS_INVALID_UID 0
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __TFM_ITS_DEFS_H__ */