ARM: sun8i: Add SMP support for the Allwinner A23

The A23 is a dual Cortex-A7. Add the logic to use the IPs used to
control the CPU configuration and the CPU power so that we can
bring up secondary CPUs at boot.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>