Now that libata is smart enough to handle both soft and hard resets,
add hardreset method.  Note that sil24 hardreset doesn't supply
signature; still, the new reset mechanism can make good use of it.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>