[BLOCK] dm-crypt: benbi IV, big endian narrow block count for LRW-32-AES

LRW-32-AES needs a certain IV. This IV should be provided dm-crypt.
The block cipher mode could, in principle generate the correct IV from
the plain IV, but I think that it is cleaner to supply the right IV
directly.

The sector -> narrow block calculation uses a shift for performance reasons.
This shift is computed in .ctr and stored in cc->iv_gen_private (as a void *).

Signed-off-by: Rik Snel <rsnel@cube.dyndns.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>