onenand: add yaffs write command

Yaffs image require to use the oob to store some info, so when we
burn the yaffs image, we need to also write the image's oob part
into flash.

This patch add addition suffix to onenand write to give the uboot
the power to directly burn the yaffs image to onenand.

Signed-off-by: Lei Wen <leiwen@marvell.com>