[ARM] mv78xx0: wire up ethernet error interrupt

Wire up the ethernet port's error interrupt so that the
mv643xx_eth driver can sleep for SMI event completion instead of
having to busy-wait for it.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>