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/p3p440.h b/include/configs/p3p440.h
index 1dc8656..729ca6a 100644
--- a/include/configs/p3p440.h
+++ b/include/configs/p3p440.h
@@ -158,6 +158,7 @@
 #define CONFIG_LOADS_ECHO	1	/* echo on for serial download	*/
 #define CONFIG_SYS_LOADS_BAUD_CHANGE	1	/* allow baudrate change	*/
 
+#define CONFIG_PPC4xx_EMAC
 #define CONFIG_MII		1	/* MII PHY management		*/
 #define CONFIG_PHY_ADDR		0x1c	/* PHY address			*/
 #define CONFIG_HAS_ETH1