dt-bindings: devfreq: tegra30-actmon: Add cooling-cells

The ACTMON watches activity of memory clients. Decisions about a minimum
required frequency are made based on the info from ACTMON. We can use
ACTMON as a thermal cooling device by limiting the required frequency.
Document new cooling-cells property of NVIDIA Tegra ACTMON hardware unit.

Reviewed-by: Rob Herring <[e-mail]>
Acked-by: Chanwoo Choi <[e-mail]>
Acked-by: Thierry Reding <[e-mail]>
Signed-off-by: Dmitry Osipenko <[e-mail]>
Signed-off-by: Chanwoo Choi <[e-mail]>

Documentation/devicetree/bindings/devfreq/nvidia,tegra30-actmon.yaml

···
       Should contain freqs and voltages and opp-supported-hw property, which
       is a bitfield indicating SoC speedo ID mask.
 
+  "#cooling-cells":
+    const: 2
+
 required:
   - compatible
   - reg
···
   - interconnects
   - interconnect-names
   - operating-points-v2
+  - "#cooling-cells"
 
 additionalProperties: false
 
···
         operating-points-v2 = <&dvfs_opp_table>;
         interconnects = <&mc TEGRA30_MC_MPCORER &emc>;
         interconnect-names = "cpu-read";
+        #cooling-cells = <2>;
     };