zynq: Enable CONFIG_DEFAULT_DEVICE_TREE

Enabled default dts files on respective pre-board config
files this is way MAKEALL will works. and it's upto user
to build specific dts by specifying at build time.

$ make zynq_zc70x_config
$ make -->  with default dts zynq-zc702.dts
or
$ make DEVICE_TREE=zynq-zc702 --> Same configuration with zynq-zc706.dts

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
diff --git a/include/configs/zynq_zc70x.h b/include/configs/zynq_zc70x.h
index 0a7fa97..673660e 100644
--- a/include/configs/zynq_zc70x.h
+++ b/include/configs/zynq_zc70x.h
@@ -22,6 +22,7 @@
 #define CONFIG_ZYNQ_I2C0
 #define CONFIG_ZYNQ_EEPROM
 #define CONFIG_ZYNQ_BOOT_FREEBSD
+#define CONFIG_DEFAULT_DEVICE_TREE	zynq-zc702
 
 #include <configs/zynq-common.h>