image_types bbclass: use compression framework for jffs2 sum images
I got hit by a missing dependency in generation of sum.jffs2 images - at
runtime, when images are generated using bitbake pool, it is possible
for sum.jffs2 image to be scheduled for generation before jffs2 image is
fully generated.
Insted of adding additional hacks, reimplement sum.jffs2 generation as a
compression scheme on top of plain jffs2 images. For now support for
sum.jffs2 images is left in, it will be removed by the subsequent
commit.
Signed-off-by: Dmitry Eremin-Solenikov <dmitry_eremin@mentor.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
