ARM: at91/dt: add support for kizbox2

Add DT file for Kizbox 2 board.
This board is based on Atmel's SAMA5D31 Cortex-A5 SoC.

Signed-off-by: Gaël PORTAY <g.portay@overkiz.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>