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/netstal-common.h b/include/configs/netstal-common.h
index 1fa4b00..0a75794 100644
--- a/include/configs/netstal-common.h
+++ b/include/configs/netstal-common.h
@@ -58,6 +58,7 @@
 /*
  * Ethernet/EMAC/PHY
  */
+#define CONFIG_PPC4xx_EMAC
 #define CONFIG_MII			/* MII PHY management		*/
 #define CONFIG_PHY_ADDR		1	/* PHY address			*/
 #if defined(CONFIG_440)