ARM: Kirkwood: Add support for another ZyXEL NSA310 variant

There are a number of variants of the ZyXEL NSA310, with slightly
different LEDs, buttons and i2c devices. Add a DTS file to support one
more of these variants.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Tibor Hársszegi <tibor@harsszegi.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>