Add support for the IB-NAS6210 and IB-NAS 6220. Describe as much as
currently possible in the devicetree files, including the NAND partitions.
Use the partition scheme of the original firmware by default.

Create a board-ib62x0.c for everything else.
Signed-off-by: NSimon Baatz <gmbnomis@gmail.com>
Signed-off-by: NJason Cooper <jason@lakedaemon.net>