ARM: at91/dt: at91-kizbox: gpio-keys related changes

This:
 * fixes active level of GPIO (active high) and
 * renames buttons:
   - reset (PB_RST), and
   - mode to user (PB_USER).

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>