feat(plat/arm/css): add per-cpu power down support for warm reset

Add a new function to setup a SGI interrupt that will be used to trigger
a request for per-cpu power down when executing the PSCI SYSTEM_RESET
request. This will be used on CSS platform that require all the CPUs to
execute the CPU specific power down sequence to complete a warm reboot
sequence in which only the CPUs are power cycled.

Change-Id: I80da0f6c3cd0c5c442c82239ba1e1f773821a7f5
Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>
diff --git a/plat/arm/css/common/css_common.mk b/plat/arm/css/common/css_common.mk
index 2fbbe45..c41a1fb 100644
--- a/plat/arm/css/common/css_common.mk
+++ b/plat/arm/css/common/css_common.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2015-2022, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -88,3 +88,9 @@
 $(eval $(call assert_boolean,CSS_NON_SECURE_UART))
 $(eval $(call add_define,CSS_NON_SECURE_UART))
 
+# Process CSS_SYSTEM_GRACEFUL_RESET flag
+# This build option can be used on CSS platforms that require all the CPUs
+# to execute the CPU specific power down sequence to complete a warm reboot
+# sequence in which only the CPUs are power cycled.
+CSS_SYSTEM_GRACEFUL_RESET	:= 0
+$(eval $(call add_define,CSS_SYSTEM_GRACEFUL_RESET))