mtd: rawnand: micron: allow forced on-die ECC

Some Micron NAND chips have on-die ECC forceably enabled. Allow such
chips to be used as long as the controller has set chip->ecc.mode to
NAND_ECC_ON_DIE.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>