crypto: ghash - Add GHASH digest algorithm for GCM

GHASH is implemented as a shash algorithm. The actual implementation
is copied from gcm.c. This makes it possible to add
architecture/hardware accelerated GHASH implementation.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/Makefile b/crypto/Makefile
index 3c961b4..c2ca721 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -82,6 +82,7 @@
 obj-$(CONFIG_CRYPTO_RNG2) += krng.o
 obj-$(CONFIG_CRYPTO_ANSI_CPRNG) += ansi_cprng.o
 obj-$(CONFIG_CRYPTO_TEST) += tcrypt.o
+obj-$(CONFIG_CRYPTO_GHASH) += ghash-generic.o
 
 #
 # generic algorithms and the async_tx api