plat: xilinx: versal: Add support of register notifier

Add support of register notifier.

Signed-off-by: Tejas Patel <tejas.patel@xilinx.com>
Signed-off-by: Rajan Vaja <rajan.vaja@xilinx.com>
Change-Id: I41ef4c63abcc9aee552790b843adb25a5fd0c23e
diff --git a/plat/xilinx/versal/pm_service/pm_defs.h b/plat/xilinx/versal/pm_service/pm_defs.h
index 5f59ba7..793f750 100644
--- a/plat/xilinx/versal/pm_service/pm_defs.h
+++ b/plat/xilinx/versal/pm_service/pm_defs.h
@@ -45,6 +45,7 @@
 #define PM_GET_API_VERSION		1U
 #define PM_GET_DEVICE_STATUS		3U
 #define PM_GET_OP_CHARACTERISTIC	4U
+#define PM_REGISTER_NOTIFIER		5U
 #define PM_REQ_SUSPEND			6U
 #define PM_SELF_SUSPEND			7U
 #define PM_FORCE_POWERDOWN		8U