crypto: gcm - Use GHASH digest algorithm

Remove the dedicated GHASH implementation in GCM, and uses the GHASH
digest algorithm instead. This will make GCM uses hardware accelerated
GHASH implementation automatically if available.

ahash instead of shash interface is used, because some hardware
accelerated GHASH implementation needs asynchronous interface.
Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -157,7 +157,7 @@ config CRYPTO_GCM
 	tristate "GCM/GMAC support"
 	select CRYPTO_CTR
 	select CRYPTO_AEAD
-	select CRYPTO_GF128MUL
+	select CRYPTO_GHASH
 	help
 	  Support for Galois/Counter Mode (GCM) and Galois Message
 	  Authentication Code (GMAC). Required for IPSec.