The only user of akcipher does not use SG lists.  Therefore forcing
users to use SG lists only results unnecessary overhead.  Add a new
interface that supports arbitrary kernel pointers.

For the time being the copy will be performed unconditionally.  But
this will go away once the underlying interface is updated.

Note also that only encryption and decryption is addressed by this
patch as sign/verify will go into a new interface (sig).
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>