Add support CONFIG_UEC_ETH3 in MPC83xx

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
diff --git a/net/eth.c b/net/eth.c
index 3373a05..d2fced8 100644
--- a/net/eth.c
+++ b/net/eth.c
@@ -214,6 +214,9 @@
 #if defined(CONFIG_UEC_ETH2)
 	uec_initialize(1);
 #endif
+#if defined(CONFIG_UEC_ETH3)
+	uec_initialize(2);
+#endif
 
 #if defined(FEC_ENET) || defined(CONFIG_ETHER_ON_FCC)
 	fec_initialize(bis);