crypto: cryptd - convert to new way of freeing instances

Convert the "cryptd" template to the new way of freeing instances, where
a ->free() method is installed to the instance struct itself.  This
replaces the weakly-typed method crypto_template::free().

This will allow removing support for the old way of freeing instances.

Note that the 'default' case in cryptd_free() was already unreachable.
So, we aren't missing anything by keeping only the ahash and aead parts.

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