crypto: nx - Moving limit and bound logic in CTR and fix IV vector

The previous limits were estimated locally in a single step
basead on bound values, however it was not correct since
when given certain scatterlist the function nx_build_sg_lists
was consuming more sg entries than allocated causing a
memory corruption and crashes.

- This patch removes the old logic and replaces it into nx_sg_build_lists
in order to build a correct nx_sg list using the correct sg_max limit
and bounds.

IV vector was not set correctly to zero causing ctr crash in tcrypt tests.

- Fixed setting IV vector  bits to zero.

Signed-off-by: Leonidas S. Barbosa <leosilva@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>