dt-bindings: power: rockchip: Convert to json-schema

Convert the soc/rockchip/power_domain.txt binding document to
json-schema and move to the power bindings directory.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210417112952.8516-14-jbx6244@gmail.com


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