crypto: sm3 - export crypto_sm3_final function

Both crypto_sm3_update and crypto_sm3_finup have been
exported, exporting crypto_sm3_final, to avoid having to
use crypto_sm3_finup(desc, NULL, 0, dgst) to calculate
the hash in some cases.

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Tested-by: Xufeng Zhang <yunbo.xufeng@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>