dt-bindings: power: add rk3568-pmu-io-domain support

Add binding for the RK3568 along a SoC-specific description of
voltage supplies.

Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>
[add soc-specific section]
Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210805120107.27007-2-michael.riesch@wolfvision.net


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