crypto: api - Move alg destroy work from instance to template

Commit 9ae4577b ("crypto: api - Use work queue in
crypto_destroy_instance") introduced a work struct to free an
instance after the last user goes away.

Move the delayed work from the instance into its template so that
when the template is unregistered it can ensure that all its
instances have been freed before returning.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>