Add the gcm_context_data structure to the avx asm routines.
This will be necessary to support both 256 bit keys and
scatter/gather.

The pre-computed HashKeys are now stored in the gcm_context_data
struct, which is expanded to hold the greater number of hashkeys
necessary for avx.

Loads and stores to the new struct are always done unlaligned to
avoid compiler issues, see e5b954e8 "Use unaligned loads from
gcm_context_data"
Signed-off-by: Dave Watson <davejwatson@fb.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>