mtd: rawnand: cadence: get meta data size from registers

Add checking size of BCH meta data size in capabilities registers
instead of using fixed value. BCH meta data is used to keep data
from NAND flash OOB area.

Signed-off-by: Piotr Sroka <piotrs@cadence.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1581328530-29966-1-git-send-email-piotrs@cadence.com