dt-bindings: reset: syscon-reboot: Add reg property

The syscon-reboot binding used 'offset' for historical reasons. Having a
reg property is appropriate when these nodes are children of a MMIO bus.
Add a reg property and modify the constraints so that one of 'reg' or
'offset' is expected.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20241015225948.3971924-2-chris.packham@alliedtelesis.co.nz
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

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

@@ -31,6 +31,10 @@ properties:
     $ref: /schemas/types.yaml#/definitions/uint32
     description: Offset in the register map for the reboot register (in bytes).
 
+  reg:
+    maxItems: 1
+    description: Base address and size for the reboot register.
+
   regmap:
     $ref: /schemas/types.yaml#/definitions/phandle
     deprecated: true
@@ -45,9 +49,14 @@ properties:
   priority:
     default: 192
 
+oneOf:
+  - required:
+      - offset
+  - required:
+      - reg
+
 required:
   - compatible
-  - offset
 
 additionalProperties: false