xilinx: common: Move ATF handover to common file

ATF handover can be used by Xilinx platforms, so move it to common
file from platform specific files.

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@xilinx.com>
Change-Id: I5f0839351f534619de581d1953c8427a079487e0
diff --git a/plat/xilinx/zynqmp/platform.mk b/plat/xilinx/zynqmp/platform.mk
index de4bf3a..44f20f6 100644
--- a/plat/xilinx/zynqmp/platform.mk
+++ b/plat/xilinx/zynqmp/platform.mk
@@ -82,10 +82,10 @@
 				plat/common/plat_psci_common.c			\
 				plat/xilinx/common/ipi_mailbox_service/ipi_mailbox_svc.c \
 				plat/xilinx/common/pm_service/pm_ipi.c		\
+				plat/xilinx/common/plat_startup.c		\
 				plat/xilinx/zynqmp/bl31_zynqmp_setup.c		\
 				plat/xilinx/zynqmp/plat_psci.c			\
 				plat/xilinx/zynqmp/plat_zynqmp.c		\
-				plat/xilinx/zynqmp/plat_startup.c		\
 				plat/xilinx/zynqmp/plat_topology.c		\
 				plat/xilinx/zynqmp/sip_svc_setup.c		\
 				plat/xilinx/zynqmp/pm_service/pm_svc_main.c	\