dts: bindings: add bindings zephyr,flash-disk

Add bindings to describe a block storage device based on flash map
partition.

Co-authored-by: Johann Fischer <johann.fischer@nordicsemi.no>
Signed-off-by: Tomasz Moń <tomasz.mon@nordicsemi.no>

dts/bindings/misc/zephyr,flash-disk.yaml

@@ -0,0 +1,38 @@
+# Copyright (c) 2022 Nordic Semiconductor ASA
+# SPDX-License-Identifier: Apache-2.0
+
+description: Block storage device on flash partition
+
+compatible: "zephyr,flash-disk"
+
+include: base.yaml
+
+properties:
+    partition:
+      type: phandle
+      required: true
+      description: |
+        Backing storage flash map partition.
+
+    disk-name:
+      type: string
+      required: true
+      description: |
+        Disk name.
+
+    sector-size:
+      type: int
+      required: false
+      default: 512
+      description: |
+        Emulated block device sector size in bytes.
+
+    cache-size:
+      type: int
+      required: true
+      description: |
+        Size of statically allocated buffer size in bytes. The size should be
+        adequately chosen. On storage backends with uniform erase-blocks it
+        should be at least the erase-block-size, on storage backends with
+        non-uniform erase-blocks it should be at least the largest
+        erase-block-size.