mtd: nand: Cleanup flags and fields for bad block marker position

Now that we have moved the information to the chip level, let's
remove all the unused flags and fields.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>