dt-bindings: mtd: add a common label property to all mtd devices

This can be used to easily identify a specific chip on a system with
multiple chips.
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

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 */
+	};