crypto: sha512_generic - add cra_priority

sha512-generic and sha384-generic had a cra_priority of 0, so it wasn't
possible to have a lower priority SHA-512 or SHA-384 implementation, as
is desired for sha512_mb which is only useful under certain workloads
and is otherwise extremely slow.  Change them to priority 100, which is
the priority used for many of the other generic algorithms.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>