refactor(context mgmt): add cm_prepare_el3_exit_ns function

As part of the RFC:
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/13651,
this patch adds the 'cm_prepare_el3_exit_ns' function. The function is
a wrapper to 'cm_prepare_el3_exit' function for Non-secure state.

When EL2 sysregs context exists (CTX_INCLUDE_EL2_REGS is
enabled) EL1 and EL2 sysreg values are restored from the context
instead of directly updating the registers.

Signed-off-by: Zelalem Aweke <zelalem.aweke@arm.com>
Change-Id: I9b071030576bb05500d54090e2a03b3f125d1653
diff --git a/lib/el3_runtime/aarch32/context_mgmt.c b/lib/el3_runtime/aarch32/context_mgmt.c
index 3ef378c..af8edf5 100644
--- a/lib/el3_runtime/aarch32/context_mgmt.c
+++ b/lib/el3_runtime/aarch32/context_mgmt.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016-2021, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2016-2022, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -332,3 +332,12 @@
 		enable_extensions_nonsecure(el2_unused);
 	}
 }
+
+/*******************************************************************************
+ * This function is used to exit to Non-secure world. It simply calls the
+ * cm_prepare_el3_exit function for AArch32.
+ ******************************************************************************/
+void cm_prepare_el3_exit_ns(void)
+{
+	cm_prepare_el3_exit(NON_SECURE);
+}