As the padlock driver for SHA uses a software fallback to perform
partial hashing, it must implement custom import/export functions.
Otherwise hmac which depends on import/export for prehashing will
not work with padlock-sha.
Reported-by: NWolfgang Walter <wolfgang.walter@stwm.de>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>