ARM: dts: rockchip: add io-domains node to rk3188.dtsi

The compatible string below was added to
rockchip-io-domain.txt, but never added to the device tree,
so add a io-domains node to rk3188.dtsi

"rockchip,rk3188-io-voltage-domain"

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Link: https://lore.kernel.org/r/20210625111746.6269-3-jbx6244@gmail.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>