mtd: nand: mtk: add ->setup_data_interface() hook

Currently, we use the fixed ACC timing 0x10804211. This is not the best
setting for each case. Actually, MTK NAND controller can adapt ACC timings
dynamically according to nfi clock frequence.
Implement the ->setup_data_interface() hook to optimize driver performance.

Signed-off-by: Xiaolei Li <xiaolei.li@mediatek.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>