crypto: img-hash - Add support for export and import

Currently the img-hash accelerator does not probe
successfully due to a change in the checks made during
registration with the crypto framework. This is due to
import and export functions not being defined. Correct
this.

Signed-off-by: James Hartley <james.hartley@imgtec.com>
Signed-off-by: Will Thomas <will.thomas@imgtec.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>