crypto: sha3-generic - export init/update/final routines

To allow accelerated implementations to fall back to the generic
routines, e.g., in contexts where a SIMD based implementation is
not allowed to run, expose the generic SHA3 init/update/final
routines to other modules.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>