ARM: imx6: add ZII RDU2 boards

[Nikita Yushchenko]

> This adds support for the Zodiac Inflight Innovations RDU2 board,
> which has both a Quad and a QuadPlus variant.
> 
> The board supports different panels, with the bootloader patching
> in the correct compatible, depending on the hardware configuration.
> 
> Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>

Tested-by: Nikita Yushchenko <nikita.yoush at cogentembedded.com>