ARM: rockchip: add smp bringup code

This adds the necessary smp-operations and startup code to use
additional cores on Rockchip SoCs.

We currently hog the power management unit in the smp code, as it is
necessary to control the power to the cpu core and nothing else is
currently using it, so a generic implementation can be done later.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Ulrich Prinz <ulrich.prinz@googlemail.com>