crypto: picoxcell - Convert to new AEAD interface

This patch converts picoxcell to the new AEAD interface.  IV
generation has been removed since it's equivalent to a software
implementation.

As picoxcell cannot handle SG lists longer than 16 elements,
this patch has made the software fallback mandatory.  If an SG
list comes in that exceeds the limit, we will simply use the
fallback.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>