nand: refactor the config_nand_ooblayout() function for large page.

We reorganize the function by different ECC patch:
1. for PMECC path, the code can be reused for different pagesize nand.
2. for Software ECC path, we do different for different pagesize.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Wenyou Yang <wenyou.yang@atmel.com>
nand: In software ECC, if oobsize > 128 bytes, just use 128-byte oob schema

It also print a error message for the not support oobsize.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Wenyou Yang <wenyou.yang@atmel.com>
nand: increase the max oobsize to support 8k-page nand flash

As 8k-page nand has 448 bytes oob, to support larger than 255-byte
oob, we should change oobsize type from 'char' to 'short'.
meanwhile, all the fields of ooblayout should change to 'short'.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
nand: add PMECC support for 8k-page nand flash

Signed-off-by: Josh Wu <josh.wu@atmel.com>