dt-bindings: mtd: add YAML schema for the generic MTD bindings

Convert MTD's common.txt to mtd.yaml.
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210424110608.15748-3-michael@walle.cc

Documentation/devicetree/bindings/mtd/common.txt

-* Common properties of all MTD devices
-
-Optional properties:
-- label: user-defined MTD device name. Can be used to assign user
-  friendly names to MTD devices (instead of the flash model or flash
-  controller based name) in order to ease flash device identification
-  and/or describe what they are used for.
-
-Example:
-
-	flash@0 {
-		label = "System-firmware";
-
-		/* flash type specific properties */
-	};
+This file has been moved to mtd.yaml.

Documentation/devicetree/bindings/mtd/mtd.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/mtd.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MTD (Memory Technology Device) Device Tree Bindings
+
+maintainers:
+  - Miquel Raynal <miquel.raynal@bootlin.com>
+  - Richard Weinberger <richard@nod.at>
+
+properties:
+  $nodename:
+    pattern: "^flash(@.*)?$"
+
+  label:
+    description:
+      User-defined MTD device name. Can be used to assign user friendly
+      names to MTD devices (instead of the flash model or flash controller
+      based name) in order to ease flash device identification and/or
+      describe what they are used for.
+
+additionalProperties: true
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        flash@0 {
+            reg = <0>;
+            compatible = "jedec,spi-nor";
+            label = "System-firmware";
+        };
+    };
+
+...