dt-bindings: mtd: add DT binding for s3c2410 flash controller

Adds the device tree bindings description for Samsung S3C2410 and
compatible NAND flash controller.

Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Sergio Prado <sergio.prado@e-labworks.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>