For writing Linux or rootfs on to NAND, the best suitable way
is to use MMC commands since MMC driver by default enabled by
mx6_common.h, hence enabled MMC commands in nand defconfigs.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>