crypto: bfin_crc - Add empty hash export and import

Crypto framework requires export/import in async hash. If driver do not
implement them, wrapper functions in framework will be used, and it will
cause error during ahash alg registration (unless one disables crypto
internal tests). To make change in framework and expose this requirement,
I will remove wrappers from crypto/ahash.c , but this can broke code which
depends on them.
Add empty hash export and import, with the same behaviour as in framework
and expose this directly in driver. This can also prevent OOPS when config
option in Cryptographic API 'Disable run-time self tests' will be enabled.

Signed-off-by: Kamil Konieczny <k.konieczny@partner.samsung.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>