Changed PPC4xx EMAC driver to require CONFIG_PPC4xx_EMAC

All in-tree IBM/AMCC PPC4xx boards using the EMAC get this new CONFIG

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
Acked-by: Stefan Roese <sr@denx.de>
diff --git a/include/configs/CMS700.h b/include/configs/CMS700.h
index d58f508..d0e2464 100644
--- a/include/configs/CMS700.h
+++ b/include/configs/CMS700.h
@@ -52,6 +52,7 @@
 
 #define CONFIG_SYS_LOADS_BAUD_CHANGE	1	/* allow baudrate change	*/
 
+#define CONFIG_PPC4xx_EMAC
 #define CONFIG_NET_MULTI	1
 #undef  CONFIG_HAS_ETH1