mtd: get the ECC info from the parameter page for ONFI nand

From the ONFI spec, we can just get the ECC info from the @ecc_bits field of
the parameter page.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Reviewed-and-tested-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>