TI:omap3: enable CONFIG_CMD_DHCP for omap3_beagle

The following patch re-enables the dhcp functionality on omap3_beagle.
It was removed with df4dbb5d when
omap3_beagle was converted to use ti_omap3_common.h. I have tested
beagleboard and beagleboard-xm with this patch and confirmed dhcp is
working.

Signed-off-by: Tyler Baker <tyler.baker@linaro.org>

include/configs/omap3_beagle.h

@@ -111,6 +111,7 @@
 #define CONFIG_CMD_LED		/* LED support			*/
 #define CONFIG_CMD_SETEXPR	/* Evaluate expressions		*/
 #define CONFIG_CMD_GPIO     /* Enable gpio command */
+#define CONFIG_CMD_DHCP
 
 #define CONFIG_VIDEO_OMAP3	/* DSS Support			*/