mtd: add a new field to mtd_info{}

mtd: add a new field to mtd_info{}

In order to implement the NAND boot for some Freescale's chips, such as
imx23/imx28/imx50/imx6, we use a tool (called kobs-ng) to burn the uboot
and some metadata to nand chip. And the ROM code will use the metadata to
configrate the BCH, and to find the uboot.

The ECC information(ecc step size, ecc strength) which is used to configrate
the BCH is part of the metadata. The kobs-ng can gets the ecc strength from
the sys node /sys/*/ecc_strength now. But it can not gets the ecc step size.

This patch adds a new field to store the ecc step size in mtd_info{}, and
it makes preparation for the next patches.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>