ARM: sunxi: Share sun6i PSCI backend with sun8i

sun8i can share the PSCI backend with sun6i. Only difference
is sun8i does not have CPU power clamp controls.

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>