crypto: aead - Add support for new AEAD implementations

This patch adds the basic structure of the new AEAD type.  Unlike
the current version, there is no longer any concept of geniv.  IV
generation will still be carried out by wrappers but they will be
normal AEAD algorithms that simply take the IPsec sequence number
as the IV.

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