uboot-imx

NAND: Subpage shift for ecc_steps equal to 16

This was originally part of Thomas Gleixner's patch for
adding support for 4KiB pages.
This is not part of the U-Boot NAND driver so updating the
driver with this to sync up with the kernel NAND driver.

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>