km/kirkwood: enable USB support and the host controller driver

Our kirkwood device embeds a USB host controller that is now used
on some boards. This enables the support of USB and the corresponding
driver.

Signed-off-by: Holger Brunck <holger.brunck@hitachi-powergrids.com>
CC: Stefan Roese <sr@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>