ARM: Kirkwood: support 98DX412x kirkwoods with pinctrl

The Marvell 98DX412x SoC embed a kirkwood variant that does not have
pinctrl support yet. Even though this kirkwood is very similar to the
88f6281, on the MPP front a lot of pins are not available. That's why a
new kirkwood pinctrl variant is needed.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>