mtd: nand: Use the new generic ECC object

Embed a generic NAND ECC high-level object in the nand_device
structure to carry all the ECC engine configuration/data.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200827085208.16276-16-miquel.raynal@bootlin.com