feat(zynqmp): add hooks for custom runtime setup

Add runtime setup hooks (via custom_runtime_setup()) for low level
operations related to setting up the system to correct state.

Change-Id: I4af7050dba2ee2446366d482bef5f5c5dde4bddf
Signed-off-by: Amit Nagal <amit.nagal@amd.com>
Signed-off-by: Akshay Belsare <akshay.belsare@amd.com>
diff --git a/plat/xilinx/zynqmp/custom_sip_svc.c b/plat/xilinx/zynqmp/custom_sip_svc.c
index fbb0a33..7ffffd2 100644
--- a/plat/xilinx/zynqmp/custom_sip_svc.c
+++ b/plat/xilinx/zynqmp/custom_sip_svc.c
@@ -23,3 +23,7 @@
 void custom_mmap_add(void)
 {
 }
+
+void custom_runtime_setup(void)
+{
+}