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 <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Heiko Stuebner <[e-mail]>

Documentation/devicetree/bindings/clock/rockchip,rk3568-cru.yaml

···
   "#reset-cells":
     const: 1
 
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    const: xin24m
+
+  rockchip,grf:
+    $ref: /schemas/types.yaml#/definitions/phandle
+    description:
+      Phandle to the syscon managing the "general register files" (GRF),
+      if missing pll rates are not changeable, due to the missing pll
+      lock status.
+
 required:
   - compatible
   - reg