crypto: api - add a helper to (un)register a array of templates

This patch add a helper to (un)register a array of templates. The
following patches will use this helper to simplify the code.

Signed-off-by: Xiongfeng Wang <xiongfeng.wang@linaro.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>