dt-bindings: thermal: cooling-devices: Update support for 3 cells cooling device

Extend the thermal cooling device binding to support a 3 cells specifier
along with the 2 cells format.

Update #cooling-cells property to enum to support both 2 and 3 arguments.

Fix pwm-fan.yaml to restrict the number of cells to 'const: 2'

Signed-off-by: Gaurav Kohli <gaurav.kohli@oss.qualcomm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@oss.qualcomm.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Link: https://patch.msgid.link/20260526140802.1059293-22-daniel.lezcano@oss.qualcomm.com

Documentation/devicetree/bindings/hwmon/pwm-fan.yaml

@@ -63,7 +63,8 @@ properties:
     description: The PWM that is used to control the fan.
     maxItems: 1
 
-  "#cooling-cells": true
+  "#cooling-cells":
+    const: 2
 
 required:
   - compatible

Documentation/devicetree/bindings/thermal/thermal-cooling-devices.yaml

@@ -44,10 +44,14 @@ select: true
 properties:
   "#cooling-cells":
     description:
-      Must be 2, in order to specify minimum and maximum cooling state used in
+      Must be 2 or 3. If 2, specifies minimum and maximum cooling state used in
       the cooling-maps reference. The first cell is the minimum cooling state
       and the second cell is the maximum cooling state requested.
-    const: 2
+      If 3, the first cell specifies the thermal mitigation device specifier
+      index for devices that support multiple thermal mitigation mechanisms.
+      The two other cells are respectively the minimum cooling state and the
+      maximum cooling state.
+    enum: [2, 3]
 
 additionalProperties: true
 

Documentation/devicetree/bindings/thermal/thermal-zones.yaml

@@ -211,7 +211,8 @@ patternProperties:
                   device. Using the THERMAL_NO_LIMIT (-1UL) constant in the
                   cooling-device phandle limit specifier lets the framework
                   use the minimum and maximum cooling state for that cooling
-                  device automatically.
+                  device automatically. If three arguments are specified,
+                  the first argument is the cooling device specifier.
 
               contribution:
                 $ref: /schemas/types.yaml#/definitions/uint32