ARM: dts: ixp4xx: Add device trees for Coyote and IXDPG425

This adds device trees for the ADI Engineering Coyote and the
Intel IXDPG425 reference design. The ethernet set-up on the
IXDPG425 is a bit dubious because I think it uses a DSA
switch chip, but this is a good as it gets right now.

The Coyote boardfile claims an IDE port exist at 0xFFFE1000
but the implementation does not use this. If you have the
board and can/want to test, please contact me.

Cc: Deepak Saxena <dsaxena@plexity.net>
Cc: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Cc: Zoltan HERPAI <wigyori@uid0.hu>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>