ARM: dts: Fix up the IXP4xx ethernet nodes

All of IXP4xx SoCs has an EthA at 0xc800c000 so move this
from the IXP[56]x to the IXP4xx DTSI.

Then add the second ethernet port on the Cambria GW2358-4
on EthA.

Reported-by: Zoltan HERPAI <wigyori@uid0.hu>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>