dt-bindings: mtd: add binding for BCM4908 partitions

BCM4908 uses fixed partitions layout but function of some partitions may
vary. Some devices use multiple firmware partitions and those partitions
should be marked to let system discover their purpose.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Richard Weinberger <richard@nod.at>

Documentation/devicetree/bindings/mtd/partitions/brcm,bcm4908-partitions.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/brcm,bcm4908-partitions.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom BCM4908 partitioning
+
+description: |
+  Broadcom BCM4908 CFE bootloader supports 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: brcm,bcm4908-partitions
+
+  "#address-cells":
+    enum: [ 1, 2 ]
+
+  "#size-cells":
+    enum: [ 1, 2 ]
+
+patternProperties:
+  "^partition@[0-9a-f]+$":
+    $ref: "partition.yaml#"
+    properties:
+      compatible:
+        const: brcm,bcm4908-firmware
+    unevaluatedProperties: false
+
+required:
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    partitions {
+        compatible = "brcm,bcm4908-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+            label = "cferom";
+            reg = <0x0 0x100000>;
+        };
+
+        partition@100000 {
+            compatible = "brcm,bcm4908-firmware";
+            reg = <0x100000 0xf00000>;
+        };
+
+        partition@1000000 {
+            compatible = "brcm,bcm4908-firmware";
+            reg = <0x1000000 0xf00000>;
+        };
+
+        partition@1f00000 {
+            label = "calibration";
+            reg = <0x1f00000 0x100000>;
+        };
+    };