kirkwood: add support for Linksys EA4500

Support is added only for kernel 3.14 - do not show it until
the switch is made.

Following uboot env changes are needed to make it work on stock uboot:

target/linux/kirkwood/base-files/etc/uci-defaults/02_network

@@ -1,6 +1,6 @@
 #!/bin/sh
 #
-# Copyright (C) 2012-2013 OpenWrt.org
+# Copyright (C) 2012-2014 OpenWrt.org
 #
 
 [ -e /etc/config/network ] && exit 0
@@ -37,6 +37,9 @@ case "`cat /proc/device-tree/model`" in
 "Cloud Engines Pogoplug E02")
 	set_lan_dhcp "eth0"
 	;;
+"Linksys EA4500")
+	ucidef_set_interfaces_lan_wan "eth0" "eth1"
+	;;
 *)
 	ucidef_set_interface_lan "eth0"
 	;;