128bit is a common blocksize in linux kernel cryptography, so it helps to
centralize some common operations.

The code, while mostly trivial, is based on a header file mode_hdr.h in
http://fp.gladman.plus.com/AES/modes.vc8.19-06-06.zip

The original copyright (and GPL statement) of the original author,
Dr Brian Gladman, is preserved.
Signed-off-by: Rik Snel <rsnel@cube.dyndns.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>