82xx, mgcoge: fix compile error

With actual u-boot compiling the mgcoge port fails, because
since commit ba705b5b1a it is
necessary to define CONFIG_NET_MULTI.

Seems to me the mgcoge port is the only actual existing 8260
port who uses CONFIG_ETHER_ON_SCC, so no other 8260 port needed
to be fixed.

Signed-off-by: Heiko Schocher <hs@denx.de>

include/configs/mgcoge.h

@@ -64,6 +64,7 @@
 #define	CONFIG_ETHER_ON_SCC		/* Ethernet is on SCC */
 #undef	CONFIG_ETHER_ON_FCC		/* Ethernet is not on FCC     */
 #undef	CONFIG_ETHER_NONE		/* No external Ethernet   */
+#define CONFIG_NET_MULTI	1
 
 #define CONFIG_ETHER_INDEX	4
 #define CONFIG_SYS_SCC_TOUT_LOOP	10000000