dt-bindings: arm: cpus: Add a power-domain-name for a performance-domain

When an CPU's performance domain is managed through the SCMI firmware,
let's enable us describe this as a consumer of a power-domain provider,
which is the de-facto standard to use for performance domains. In this
case, let's specify a corresponding power-domain-name, to point out the
corresponding index for it.

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
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230825112633.236607-9-ulf.hansson@linaro.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Documentation/devicetree/bindings/arm/cpus.yaml

@@ -308,7 +308,9 @@ properties:
       power-domains property.
 
       For PSCI based platforms, the name corresponding to the index of the PSCI
-      PM domain provider, must be "psci".
+      PM domain provider, must be "psci". For SCMI based platforms, the name
+      corresponding to the index of an SCMI performance domain provider, must be
+      "perf".
 
   qcom,saw:
     $ref: /schemas/types.yaml#/definitions/phandle