power: reset: at91-reset: introduce struct at91_reset_data

Introduce struct at91_reset_data to be able to provide per SoC
data. At the moment this being only notifier callback.

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