Some devices ship with NAND images that use BCH ECC. Let the driver know
about that ECC mode so that it can be selected by machine files.

Signed-off-by: Thomas Hebb <tommyhebb@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46022 3c298f89-4303-0410-b956-a3cf2f4a3e73