watchdog: sunxi_wdt: Add support for D1

watchdog: sunxi_wdt: Add support for D1

D1 adds a key field to the "CFG" and "MODE" registers, that must be set
to change the other bits. Add logic to set the key when updating those
registers.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210902225750.29313-4-samuel@sholland.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>