The current support for the ZII Dev Boards time out on eth1 when
booting from net, which takes a while:

    Booting entry 'net'
    eth0: 100Mbps full duplex link detected
    T T T eth0: DHCP client bound to address 192.168.203.22
    WARNING: eth1: No MAC address set. Using random address 3a:e8:f7:52:55:6d
    T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T
    Loading ARM Linux zImage '/mnt/tftp/none-linux-zii-dev-rev-b-2'

eth1 is the DSA master interface and has no use within barebox,
so disable the interface to allow Barebox to boot right away from eth0.

Suggested-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>