fix(corstone-1000): add cpu_helpers.S to platform.mk

Add Platform related dependency in Makefile

Reviewed-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
Signed-off-by: Gauri Sahnan <Gauri.Sahnan@arm.com>
Change-Id: Idecb84233d3e0c386bf0b7f6d57cbebd38875f28
diff --git a/plat/arm/board/corstone1000/platform.mk b/plat/arm/board/corstone1000/platform.mk
index 3edffe0..dcd0df8 100644
--- a/plat/arm/board/corstone1000/platform.mk
+++ b/plat/arm/board/corstone1000/platform.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2021-2022, Arm Limited and Contributors. All rights reserved.
+# Copyright (c) 2021-2023, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -43,6 +43,7 @@
 				plat/arm/board/corstone1000/common/corstone1000_err.c		\
 				plat/arm/board/corstone1000/common/corstone1000_trusted_boot.c	\
 				lib/utils/mem_region.c					\
+				lib/cpus/aarch64/cpu_helpers.S \
 				plat/arm/board/corstone1000/common/corstone1000_helpers.S		\
 				plat/arm/board/corstone1000/common/corstone1000_plat.c		\
 				plat/arm/board/corstone1000/common/corstone1000_bl2_mem_params_desc.c \