mtd: nand: increase the max eccpos size to 448

Increase the max eccpos size to support 8k page nand.

Signed-off-by: Raphal Poggi <poggi.raph@gmail.com>
mtd: atmel_nand: enable PMECC for 8k page nand

Enable the PMECC to support 8k page.

Signed-off-by: Raphal Poggi <poggi.raph@gmail.com>