mtd: s3c2410: parse the device configuration from OF node

Allows configuring Samsung's s3c2410 memory controller using a
devicetree.

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