dt-bindings: mtd: add binding for Linksys Northstar partitions

Linksys on Broadcom Northstar devices uses fixed flash layout with
multiple firmware partitions.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210312134919.7767-1-zajec5@gmail.com

Documentation/devicetree/bindings/mtd/partitions/linksys,ns-partitions.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/linksys,ns-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Linksys Northstar partitioning
+
+description: |
+  Linksys devices based on Broadcom Northstar architecture often use two
+  firmware partitions. One is used for regular booting, the other is treated as
+  fallback.
+
+  This binding allows defining all fixed partitions and marking those containing
+  firmware. System can use that information e.g. for booting or flashing
+  purposes.
+
+maintainers:
+  - Rafał Miłecki <rafal@milecki.pl>
+
+properties:
+  compatible:
+    const: linksys,ns-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: "partition.yaml#"
+    properties:
+      compatible:
+        items:
+          - const: linksys,ns-firmware
+          - const: brcm,trx
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "linksys,ns-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+            label = "boot";
+            reg = <0x0 0x100000>;
+            read-only;
+        };
+
+        partition@100000 {
+            label = "nvram";
+            reg = <0x100000 0x100000>;
+        };
+
+        partition@200000 {
+            compatible = "linksys,ns-firmware", "brcm,trx";
+            reg = <0x200000 0xf00000>;
+        };
+
+        partition@1100000 {
+            compatible = "linksys,ns-firmware", "brcm,trx";
+            reg = <0x1100000 0xf00000>;
+        };
+    };