mtd: rawnand: Add the ->choose_interface_config() hook

This hook can be overloaded by NAND manufacturer drivers to propose
alternative timings when not following the main standards. In this
case, the manufacturer drivers is responsible for choosing the best
interface configuration that fits both the controller and chip
capabilities.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200529111322.7184-23-miquel.raynal@bootlin.com