ARM: kirkwood: Define DNS-320/DNS-325 NAND in fdt

Use devicetree to define NAND partitions. Use D-link partition scheme by
default, to be vaguely compatible with their userland.

Changes since last submission (V4):-
* Don't add NAND support then throw it away immediately after [Grant Likely]

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Jamie Lentin <jm@lentin.co.uk>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>