Convert CONFIG_SYS_NAND_DRIVER_ECC_LAYOUT to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_NAND_DRIVER_ECC_LAYOUT

In order to do this conversion, expose this option to the user and
use "save" not "safe" in the text.

Signed-off-by: Tom Rini <trini@konsulko.com>