dt-binding: clock: Document rockchip, rk3568-cru bindings

Document the device tree bindings of the rockchip Rk3568 SoC
clock driver in Documentation/devicetree/bindings/clock/rockchip,rk3568-cru.yaml.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20210315085608.16010-2-zhangqing@rock-chips.com


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