Add GCM/GMAC support to cryptoapi.

GCM (Galois/Counter Mode) is an AEAD mode of operations for any block cipher
with a block size of 16.  The typical example is AES-GCM.
Signed-off-by: Mikko Herranen <mh1@iki.fi>
Reviewed-by: Mika Kukkonen <mika.kukkonen@nsn.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>