[ARM] Orion: implement power-off method for Kurobox Pro

This patch implements the communication with the microcontroller on the
Kurobox Pro and Linkstation Pro/Live boards.  This is allowing to send
the commands needed to power-off the board correctly.

Signed-off-by: Sylver Bruneau <sylver.bruneau@googlemail.com>
Acked-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>