nand: Change NAND_MAX_OOBSIZE to 218 as needed for some 4k page devices

This is needed for the MPC512x NAND driver (fsl_nfc_nand.c) which already
defines such a 4k plus 218 bytes ECC layout.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Scott Wood <scottwood@freescale.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>