crytpo: sun8i-ce - factor out prepare/unprepare from sun8i_ce_hash_run()

In order to make the ahash code more clear and modular, split the
monolithic sun8i_ce_hash_run() callback into two parts, prepare and
unprepare (therefore aligning it with the sun8i-ce skcipher code).

Signed-off-by: Ovidiu Panait <ovidiu.panait.oss@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>