MTD: nand: increase the max eccpos size to 448 to support 8k page nand

For example, Micron MT29F64G08CBAAAWP has 8192 bytes page with 448 byte
oob. It needs 24bit ecc per page.
If 24bit error correction per 1024 bytes need extra 42 bytes in oob.
That means we need eccpos array size is 336 byte.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
mtd: atmel_nand: enable PMECC support for 8k bytes page NAND flash

increase the delay to 75us to support the 8k bytes page nand flash

Signed-off-by: Josh Wu <josh.wu@atmel.com>
sama5d3xek: support larger than 4G nand flash

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