dt-bindings: mtd: partitions: u-boot: allow dynamic subpartitions

U-Boot partition may contain subpartitions. For example Broadcom
includes environment data block in the middle of its U-Boot partition.

This allows describing Broadcom's U-Boot env data and will allow
referencing its NVMEM cell in the future.

Ref: 118f3fbe ("dt-bindings: mtd: partitions: support label/name only partition")
Ref: dd638202 ("dt-bindings: mtd: partitions: add additional example for qcom,smem-part")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Link: https://lore.kernel.org/r/20221018154202.4634-1-zajec5@gmail.comSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/mtd/partitions/u-boot.yaml

@@ -27,6 +27,10 @@ properties:
           Broadcom stores environment variables inside a U-Boot partition. They
           can be identified by a custom header with magic value.
 
+patternProperties:
+  "^partition-.*$":
+    $ref: partition.yaml#
+
 unevaluatedProperties: false
 
 examples:
@@ -40,6 +44,9 @@ examples:
             compatible = "brcm,u-boot";
             reg = <0x0 0x100000>;
             label = "u-boot";
+
+            partition-u-boot-env {
+            };
         };
 
         partition@100000 {