sunxi: Implement poweroff support for axp818 pmic

Adds poweroff support for axp818 pmic.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
3 files changed