image_types.bbclass: disable cleanmarkers for jffs2 images
* Add '-n' to suppress cleanmarker nodes since jffs2
* is usually used for NAND flash and the cleanmarkers are created in
* the OOB area by flash_eraseall -j
*
* From man pages: -n, --no-cleanmarkers
* Do not write cleanmarker nodes to the beginning of each erase block.
* This option can be useful for creating JFFS2 images for use on NAND flash,
* and for creating images which are to be used on a variety of hardware with differing eraseblock sizes.
Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
