crypto: atmel-sha - make atmel_sha_done_task more generic

This patch is a transitional patch. It updates atmel_sha_done_task() to
make it more generic. Indeed, it adds a new .resume() member in the
atmel_sha_dev structure. This hook is called from atmel_sha_done_task()
to resume processing an asynchronous request.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>