ARM: Kirkwood: DT version of OpenRD boards

Create dts files for the Marvell OpenRD boards, and C code for
handling the kernel command line and enabling extra hardware.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
ARM: Kirkwood: Enable OpenRD DT in kirkwood_defconfig

Enable support for the Marvell OpenRD via DT.

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