ARM: dts: rockchip: add cpu and gpu regulators to rk3288-evb-act8846

The evaluation board using the act8846 as main pmic uses two additional
regulators to provide the cpu and gpu voltage. Add these and also add
the link to cpu supply from vdd_cpu.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Daniel Lezcano <daniel.lezcano@linaro.org>