mtd: add ECC info for nand_flash_dev{}

mtd: add ECC info for nand_flash_dev{}

Add an instance of an anonymous struct to store the ECC info for full id
nand chips.
	@ecc.strength_ds: ECC correctability from the datasheet.
	@ecc.step_ds: ECC size required by the @ecc.strength_ds,

These two fields are all from the datasheet.

Also add the necessary macros to make the code simple and clean.

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