arm64: dts: rockchip: add cpu regulator for rk3328 evaluation board

RK3328 Evaluation Board use rk805 pmic, and one of the DCDCs in
rk805 is for cpu regulator, assign the cpu regulator, so the
cpufreq can work fine.

Signed-off-by: Liang Chen <cl@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>