ARM: rockchip: add support smp for rk3036

The dual-core Cortex A7 rk3036 is a bit special in that it does not allow
to control the actual powerdomain of the cpu cores, while the rest of the
smp-bringup like reset control and entry address handling stays the same.
Its bigger sibling, the quad-core rk3128 again allows powerdomain control.

So allow that case by introducing a separate smp-enable-method, that simply
disables powerdomain handling in the common code.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Xing Zheng <zhengxing@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>