mtd: mediatek: driver for MTK Smart Device

Add support for mediatek's SDG1 NFC nand controller embedded in SoC
2701

Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Tested-by: Xiaolei Li <xiaolei.li@mediatek.com>