mtd: lantiq: Add NAND support on Lantiq XWAY SoC.

The driver uses plat_nand. As the platform_device is loaded from DT, we need
to lookup the node and attach our xway specific "struct platform_nand_data"
to it.

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>