feat(ti): allow build config of low power mode support

Not all K3 platforms support low power mode, so to allow these
features to be included for platforms that do in build and
therefore reported in the PSCI caps, define K3_PM_SYSTEM_SUSPEND
flag that can be set during build that will cause appropriate
space and functionality to be included in build for system
suspend support.

Change-Id: I821fbbd5232d91de6c40f63254b855e285d9b3e8
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>

plat/ti/k3/common/plat_common.mk

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2017-2020, ARM Limited and Contributors. All rights reserved.
+# Copyright (c) 2017-2022, ARM Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -45,6 +45,10 @@ $(eval $(call add_define,K3_USART))
 K3_USART_BAUD		:=	115200
 $(eval $(call add_define,K3_USART_BAUD))
 
+# Enable system suspend modes
+K3_PM_SYSTEM_SUSPEND	:=	0
+$(eval $(call add_define,K3_PM_SYSTEM_SUSPEND))
+
 # Libraries
 include lib/xlat_tables_v2/xlat_tables.mk