crypto: sha256_generic - Add export/import support

This patch adds export/import support to sha256_generic.  The exported
type is defined by struct sha256_state, which is basically the entire
descriptor state of sha256_generic.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/include/crypto/sha.h b/include/crypto/sha.h
index 922a248..88ef5eb 100644
--- a/include/crypto/sha.h
+++ b/include/crypto/sha.h
@@ -70,4 +70,10 @@
 	u8 buffer[SHA1_BLOCK_SIZE];
 };
 
+struct sha256_state {
+	u64 count;
+	u32 state[SHA256_DIGEST_SIZE / 4];
+	u8 buf[SHA256_BLOCK_SIZE];
+};
+
 #endif