arm: at91: support for the Calao USB-A9263 board (based on AT91SAM9263)

Add support for USB-A9263 board manufactured by Calao Systems
(http://www.calao-systems.com/

).
Code is based on old U-Boot sources (2010.09) released by Calao.

Signed-off-by: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>