mtd: rawnand: Use the new ECC engine type enumeration

Mechanical switch from the legacy "mode" enumeration to the new
"engine type" enumeration in drivers and board files.

The device tree parsing is also updated to return the new enumeration
from the old strings.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200827085208.16276-11-miquel.raynal@bootlin.com