nand: mxs_nand: add API for switching different BCH layouts

On i.MX7 in a sake of reducing the disturbances caused by a neighboring
cells in the FCB page in the NAND chip, a randomizer is enabled when
reading the FCB page by ROM bootloader.

Add API for setting BCH to specific layout (and restoring it back) used by
ROM bootloader to be able to burn it in a proper way to NAND using
nandbcb command.

Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Signed-off-by: Anti Sullin <anti.sullin@artecdesign.ee>
Tested-by: Max Krummenacher <max.krummenacher@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>