ARM: sunxi: Enable PSCI for sun6i

Now that we have a PSCI backend for sun6i, enable it.

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