crypto: dh - Add DH software implementation

* Implement MPI based Diffie-Hellman under kpp API
 * Test provided uses data generad by OpenSSL

Signed-off-by: Salvatore Benedetto <salvatore.benedetto@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/Makefile b/crypto/Makefile
index 07b0f51..82897208e 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -32,6 +32,10 @@
 obj-$(CONFIG_CRYPTO_AKCIPHER2) += akcipher.o
 obj-$(CONFIG_CRYPTO_KPP2) += kpp.o
 
+dh_generic-y := dh.o
+dh_generic-y += dh_helper.o
+obj-$(CONFIG_CRYPTO_DH) += dh_generic.o
+
 $(obj)/rsapubkey-asn1.o: $(obj)/rsapubkey-asn1.c $(obj)/rsapubkey-asn1.h
 $(obj)/rsaprivkey-asn1.o: $(obj)/rsaprivkey-asn1.c $(obj)/rsaprivkey-asn1.h
 clean-files += rsapubkey-asn1.c rsapubkey-asn1.h