dt-bindings: mtd: describe the simple BCM963XX NOR flash layout

Add binding documentation for the standard CFE based BCM963XX flash
layout, found in most devices using a BCM63XX SoC with NOR flash.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

Documentation/devicetree/bindings/mtd/partitions/brcm,bcm963xx-cfe-nor-partitions.txt

+Broadcom BCM963XX CFE Loader NOR Flash Partitions
+=================================================
+
+Most Broadcom BCM63XX SoC based devices follow the Broadcom reference layout for
+NOR. The first erase block used for the CFE bootloader, the last for an
+NVRAM partition, and the remainder in-between for one to two firmware partitions
+at fixed offsets. A valid firmware partition is identified by the ImageTag
+header found at beginning of the second erase block, containing the rootfs and
+kernel offsets and sizes within the firmware partition.
+
+Required properties:
+- compatible : must be "brcm,bcm963xx-cfe-nor-partitions"
+
+Example:
+
+flash@1fc00000 {
+	compatible = "cfi-flash";
+	reg = <0x1fc00000 0x400000>;
+	bank-width = <2>;
+
+	partitions {
+		compatible = "brcm,bcm963xx-cfe-nor-partitions";
+	};
+};