This patch removes cipher.c/crypt in favour of a more generic function,
scatterwalk_walk, which can process an unlimited number of scatterlists in
parallel.
For a more in-depth description see the comments in front of
scatterwalk_walk and scatterwalk_info_init.
Changes since last patch: rewritten the comments, moved
scatterwalk_info_endtag to scatterwalk.c
Andrew, I think this patch is ready to be merged.