dt-bindings: arm: rockchip: add rk3568 compatible string to pmu.yaml

add "rockchip,rk3568-pmu", "syscon", "simple-mfd" for pmu nodes on a
rk3568 platform to pmu.ymal.
Signed-off-by: Liang Chen <cl@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210624114719.1685-2-cl@rock-chips.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

Documentation/devicetree/bindings/arm/rockchip/pmu.yaml

@@ -23,6 +23,7 @@ select:
           - rockchip,rk3066-pmu
           - rockchip,rk3288-pmu
           - rockchip,rk3399-pmu
+          - rockchip,rk3568-pmu
 
   required:
     - compatible
@@ -35,6 +36,7 @@ properties:
           - rockchip,rk3066-pmu
           - rockchip,rk3288-pmu
           - rockchip,rk3399-pmu
+          - rockchip,rk3568-pmu
       - const: syscon
       - const: simple-mfd