mtd: nand: mxs check maximum ecc that platfrom supports

Check maximum ecc strength for each platfrom to avoid the calculated ecc
exceed the limitation.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Signed-off-by: Han Xu <b45815@freescale.com>
Tested-By: Tim Harvey <tharvey at gateworks.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Acked-by: Scott Wood <scottwood@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>