ARM: at91/dt: at91-kizbox: re-size nand partitions

Re-size NAND partitions since the bootstrap is able to read volumes from an
UBI image.

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>