test(el3-runtime): check DIT is retained on exception

Add a test to check that the PSTATE bits not set in the
Aarch64.TakeException but set to a default when taking an exception to
EL3 are maintained after an exception and that changes in TSP do not
effect the PSTATE in TFTF and vice versa.

Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>
Change-Id: Id4d625c7e9cbb565ac236f844274319cc02c2335
diff --git a/include/runtime_services/secure_el1_payloads/tsp.h b/include/runtime_services/secure_el1_payloads/tsp.h
index 87ee6f7..19db911 100644
--- a/include/runtime_services/secure_el1_payloads/tsp.h
+++ b/include/runtime_services/secure_el1_payloads/tsp.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, Arm Limited. All rights reserved.
+ * Copyright (c) 2018-2022, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -32,6 +32,7 @@
 #define TSP_MUL		0x2002
 #define TSP_DIV		0x2003
 #define TSP_HANDLE_SEL1_INTR_AND_RETURN	0x2004
+#define TSP_CHECK_DIT	0x2005
 
 /*
  * Identify a TSP service from function ID filtering the last 16 bits from the