power: reset: at91-reset: introduce args member in at91_reset_data

Introduce args member in struct at91_reset_data. It stores the value
that needs to be written in mode register so that the reboot actions
to happen. With these changes samx7_restart() could be removed.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>