dt-bindings: firmware: arm,scmi: Extend bindings for protocol@13

The protocol@13 node is describing the performance scaling option for the
ARM SCMI interface, as a clock provider. This is unnecessary limiting, as
performance scaling is in many cases not limited to switching a clock's
frequency.

Therefore, let's extend the binding so the interface can be modelled as a
generic performance domain too. The common way to describe this, is to use
the power-domain DT bindings, so let's use that.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
Cc: Conor Dooley <conor+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230825112633.236607-10-ulf.hansson@linaro.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Documentation/devicetree/bindings/firmware/arm,scmi.yaml

@@ -149,8 +149,15 @@ properties:
       '#clock-cells':
         const: 1
 
-    required:
-      - '#clock-cells'
+      '#power-domain-cells':
+        const: 1
+
+    oneOf:
+      - required:
+          - '#clock-cells'
+
+      - required:
+          - '#power-domain-cells'
 
   protocol@14:
     $ref: '#/$defs/protocol-node'