dt-bindings: clock: convert rockchip,rk3308-cru.txt to YAML

Convert rockchip,rk3308-cru.txt to YAML.

Changes against original bindings:
 - Add clocks and clock-names because the device has to have
   at least one input clock.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220329184339.1134-1-jbx6244@gmail.com


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