mx25pdk: Allow booting a device tree kernel

Select CONFIG_OF_LIBFDT so that a device tree kernel can be launched.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

include/configs/mx25pdk.h

@@ -87,6 +87,7 @@
 
 /* U-Boot commands */
 #include <config_cmd_default.h>
+#define CONFIG_OF_LIBFDT
 #define CONFIG_CMD_BOOTZ
 #define CONFIG_CMD_CACHE
 #define CONFIG_CMD_MMC