dt-bindings: mtd: nvmem-cells: Inherit from MTD partitions

The aim of MTD nvmem-cells is to treat MTD partitions as NVMEM
providers. Hence, MTD partition properties are valid here. Let's
reference mtd/partition.yaml which gives us a chance to drop
"additionalProperties: true" in favor of "unevaluatedProperties:
false".
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20221114090315.848208-15-miquel.raynal@bootlin.com

Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml

@@ -17,6 +17,7 @@ maintainers:
   - Ansuel Smith <ansuelsmth@gmail.com>
 
 allOf:
+  - $ref: /schemas/mtd/partitions/partition.yaml#
   - $ref: /schemas/nvmem/nvmem.yaml#
 
 properties:
@@ -26,7 +27,7 @@ properties:
 required:
   - compatible
 
-additionalProperties: true
+unevaluatedProperties: false
 
 examples:
   - |