mx31pdk: Add DHCP command

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

include/configs/mx31pdk.h

@@ -88,6 +88,7 @@
 
 #define CONFIG_CMD_MII
 #define CONFIG_CMD_PING
+#define CONFIG_CMD_DHCP
 #define CONFIG_CMD_SPI
 #define CONFIG_CMD_DATE
 #define CONFIG_CMD_NAND