Build: Update to IAR support

Cleaned up #ifdef in secure_fw/services/tfm_spm_db.inc.template
Moved "signals" member to front of spm_partition_runtime_data_t.
The suggestion to move the aggregate types to the front turned
out to be hard to make work for both PSA and non-PSA configs.

Moved REGION_DECLARE macros to new include file,
platform/include/region.h.

Cleaned up type cast in core_test_api.c

Change-Id: I5dce1e7c019d4d7e4c14dc79be5ee2b855ad4f9e
Signed-off-by: Thomas Tornblom <thomas.tornblom@iar.com>
diff --git a/platform/include/region.h b/platform/include/region.h
new file mode 100644
index 0000000..c6ca921
--- /dev/null
+++ b/platform/include/region.h
@@ -0,0 +1,17 @@
+/*
+ * Copyright (c) 2020, Arm Limited. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ */
+
+#ifndef __REGION_H__
+#define __REGION_H__
+
+/* Macros to pick linker symbols */
+#define REGION(a, b, c) a##b##c
+#define REGION_NAME(a, b, c) REGION(a, b, c)
+#define REGION_DECLARE(a, b, c) extern uint32_t REGION_NAME(a, b, c)
+#define REGION_DECLARE_T(a, b, c, t) extern t REGION_NAME(a, b, c)
+
+#endif  /* __REGION_H__ */