arm/km: add kmnusa board support

This board is similar to portl2, but it has the u-boot environment
in a SPI NOR flash and not in an i2c eeprom like portl2 have.

Some other details:
 - IVM EEPROM is at adress: pca9547:70:9
 - PCI is enabled
 - PIGGY4 is connected via MV88E6352 simple switch. There is no phy
   between the simple switch and the kirkwood.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Gerlando Falauto <gerlando.falauto@keymile.com>
cc: Prafulla Wadaskar <prafulla@marvell.com>