added yaffs2 flash file system

This is based on bc76682d93955cfb33051beb503ad9f8a5450578 from this
git tree: git://www.aleph1.co.uk/yaffs2

yaffs2 is imported due to the fact that the spark os uses yaffs2 as filesystem.

Signed-off-by: Christian Ege <k4230r6@gmail.com>
Merge branch 'project-magpie' of github.com:project-magpie/linux-sh4-2.6.32.y into project-magpie