dt-binding: clock: Add missing rk3568 cru bindings

The rk3568 cru requires a clock input and a phandle to the grf node. Add
these bindings to clear some dtbs_check warnings.

Signed-off-by: Peter Geis <pgwipeout@gmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220511150117.113070-2-pgwipeout@gmail.com


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