crypto: aesni - Introduce gcm_context_data

Introduce a gcm_context_data struct that will be used to pass
context data between scatter/gather update calls.  It is passed
as the second argument (after crypto keys), other args are
renumbered.

Signed-off-by: Dave Watson <davejwatson@fb.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>