km/spi: add SPI configuration to KM Kirkwood device tree

In order to migrate the SPI flash interface to the driver model, the SPI
configuration needs to be added in the KM Kirkwood device tree file.

Signed-off-by: Pascal Linder <pascal.linder@edu.hefr.ch>
Signed-off-by: Holger Brunck <holger.brunck@ch.abb.com>
Signed-off-by: Stefan Roese <sr@denx.de>