ARM: dts: Drop serial 1 alias on GW7001

The Gateaway 7001 has a serial port alias for serial1, this has
proven detrimental on the WG302 so remove it on this machine
as well.

Drop in a small comment that this machine is based on IXP422.

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