ARM: sunxi: Enable PSCI for sun8i

sun8i uses the same PSCI backend as sun6i, without power clamps.
Since there is no secure SRAM, the backend is placed at the end
of DRAM.

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>