dt-bindings: power: reset: $ref reboot-mode in nvmem-reboot-mode

nvmem-reboot-mode.yaml should $ref: reboot-mode.yaml, but instead
rewrites the properties. Update so it $refs instead.

Signed-off-by: Elliot Berman <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Reviewed-by: Mukesh Ojha <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Sebastian Reichel <[e-mail]>

Documentation/devicetree/bindings/power/reset/nvmem-reboot-mode.yaml

···
     items:
       - const: reboot-mode
 
-patternProperties:
-  "^mode-.+":
-    $ref: /schemas/types.yaml#/definitions/uint32
-    description: Vendor-specific mode value written to the mode register
+allOf:
+  - $ref: reboot-mode.yaml#
 
 required:
   - compatible
   - nvmem-cells
   - nvmem-cell-names
 
-additionalProperties: false
+unevaluatedProperties: false
 
 examples:
   - |