refactor(zynqmp): use common code for prepare_dtb

use common code definition and remove zynqmp local definition
for prepare_dtb in dtb flows.

Change-Id: I362b90b96852e9afccc8a2e23d3b7f709280fba7
Signed-off-by: Amit Nagal <amit.nagal@amd.com>
diff --git a/plat/xilinx/zynqmp/platform.mk b/plat/xilinx/zynqmp/platform.mk
index 9c79855..e20cb22 100644
--- a/plat/xilinx/zynqmp/platform.mk
+++ b/plat/xilinx/zynqmp/platform.mk
@@ -127,6 +127,7 @@
 				${LIBFDT_SRCS}					\
 				plat/xilinx/common/ipi_mailbox_service/ipi_mailbox_svc.c \
 				plat/xilinx/common/plat_startup.c		\
+				plat/xilinx/common/plat_fdt.c			\
 				plat/xilinx/zynqmp/bl31_zynqmp_setup.c		\
 				plat/xilinx/zynqmp/plat_psci.c			\
 				plat/xilinx/zynqmp/plat_zynqmp.c		\