The update and final functions have lots of common action.
This patch mix them in one function.
This will give some improvements:
- This will permit asynchronous support more easily
- This will permit to use finup/digest functions with some performance
  improvements
Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>