ARM: Kirkwood: Add support for another ZyXEL NSA210 variant

There are a number of variants of the ZyXEL NSA210, with slightly
different LEDs and buttons. Add a DTS file to support one more of
these variants.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
ARM: Kirkwood: update defconfig for used i2c devices and EXT4 FS

Various kirkwood boards make use of i2c devices. Ensure the defconfig
builds them. Also, EXT4 FS is also common on NAS boxes, so include it
as well.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
ARM: Kirkwood: kirkwood-nsa310.dts add missing SOC include

Each DTS file should include the specific SOC DTSI file. This is
missing for kirkwood-nsa310.dts

Signed-off-by: Andrew Lunn <andrew@lunn.ch>