dt-bindings: firmware: arm,scmi: Add support for system power protocol

Add SCMI System Power Protocol bindings, and the protocol id is 0x12.
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Message-Id: <20240628030309.1162012-1-peng.fan@oss.nxp.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

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

@@ -145,6 +145,14 @@ properties:
     required:
       - '#power-domain-cells'
 
+  protocol@12:
+    $ref: '#/$defs/protocol-node'
+    unevaluatedProperties: false
+
+    properties:
+      reg:
+        const: 0x12
+
   protocol@13:
     $ref: '#/$defs/protocol-node'
     unevaluatedProperties: false