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/METROBOX.h b/include/configs/METROBOX.h
index c0ddd45..518173a 100644
--- a/include/configs/METROBOX.h
+++ b/include/configs/METROBOX.h
@@ -221,6 +221,7 @@
 /*-----------------------------------------------------------------------
  * Networking
  *----------------------------------------------------------------------*/
+#define CONFIG_PPC4xx_EMAC
 #define CONFIG_MII	      1		     /* MII PHY management	*/
 #define CONFIG_NET_MULTI      1
 #define CONFIG_PHY_ADDR	      0xff	     /* no phy on EMAC0		*/