imx: imx8qx: add system off support

Add system power off support for i.MX8QX,
when Linux kernel issues "poweroff" command,
TF-A will send command to inform system
controller to power off whole board according
to board design, tested on i.MX8QX MEK board.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
diff --git a/plat/imx/imx8qx/imx8qx_psci.c b/plat/imx/imx8qx/imx8qx_psci.c
index 47233dc..1e8f7fa 100644
--- a/plat/imx/imx8qx/imx8qx_psci.c
+++ b/plat/imx/imx8qx/imx8qx_psci.c
@@ -64,6 +64,7 @@
 	.pwr_domain_on = imx_pwr_domain_on,
 	.pwr_domain_on_finish = imx_pwr_domain_on_finish,
 	.validate_ns_entrypoint = imx_validate_ns_entrypoint,
+	.system_off = imx_system_off,
 };
 
 int plat_setup_psci_ops(uintptr_t sec_entrypoint,
diff --git a/plat/imx/imx8qx/platform.mk b/plat/imx/imx8qx/platform.mk
index c16ce6e..7d6e3fd 100644
--- a/plat/imx/imx8qx/platform.mk
+++ b/plat/imx/imx8qx/platform.mk
@@ -20,6 +20,7 @@
 				plat/imx/imx8qx/imx8qx_bl31_setup.c	\
 				plat/imx/imx8qx/imx8qx_psci.c		\
 				plat/imx/common/imx8_topology.c		\
+				plat/imx/common/imx8_psci.c		\
 				lib/xlat_tables/xlat_tables_common.c	\
 				lib/xlat_tables/aarch64/xlat_tables.c	\
 				lib/cpus/aarch64/cortex_a35.S		\