dt-bindings: power: syscon-poweroff: Allow "reg" property

Similar to "syscon-reset", allow using the standard "reg" property
rather than "offset".

Link: https://patch.msgid.link/20251216211556.3047726-1-robh@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/power/reset/syscon-poweroff.yaml

@@ -23,6 +23,9 @@ properties:
   compatible:
     const: syscon-poweroff
 
+  reg:
+    maxItems: 1
+
   mask:
     $ref: /schemas/types.yaml#/definitions/uint32
     description: Update only the register bits defined by the mask (32 bit).
@@ -44,7 +47,10 @@ properties:
 
 required:
   - compatible
-  - offset
+
+anyOf:
+  - required: [offset]
+  - required: [reg]
 
 additionalProperties: false