crypto: n2 - Use platform_register/unregister_drivers()

These new helpers simplify implementing multi-driver modules and
properly handle failure to register one driver by unregistering all
previously registered drivers.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>