feat(cm): test integrity of el1_ctx registers

* This patch adds support to tsp (BL32) Image, to exercise
  EL1_context registers at S-EL1.

* Adds a SMC function ID "MODIFY_EL1_CTX" to handle EL1_CTX
  registers at S-EL1 and overwrite them.

Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>
Change-Id: Id4f2b3b748f7bc9e6c9d72a2f03d50aefbfb61cb
diff --git a/services/spd/tspd/tspd_main.c b/services/spd/tspd/tspd_main.c
index 6cb4992..8ff71cc 100644
--- a/services/spd/tspd/tspd_main.c
+++ b/services/spd/tspd/tspd_main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013-2022, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2013-2024, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -575,6 +575,11 @@
 		 * of the DIT PSTATE bit.
 		 */
 	case TSP_YIELD_FID(TSP_CHECK_DIT):
+		/*
+		 * Request from non-secure client to modify the EL1
+		 * context registers.
+		 */
+	case TSP_YIELD_FID(TSP_MODIFY_EL1_CTX):
 		if (ns) {
 			/*
 			 * This is a fresh request from the non-secure client.