ARM: kirkwood: Move the nand node under the mbus node

There should be no nodes that are not children of the mbus. Move
the nand node under the mbus, and rework the board .dts files
to use an & reference to the nand node.

Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Acked-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>