[ARM] 4715/2: Ethernet support for IXDP425 boards

Adds IXDP425 platform support for two built-in 10/100 Ethernet ports.

This patch will do nothing until the actual Ethernet driver is
also included.

Signed-off-by: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>