crypto: hash - add zero length message hash for shax and md5

Some crypto drivers cannot process empty data message and return a
precalculated hash for md5/sha1/sha224/sha256.

This patch add thoses precalculated hash in include/crypto.

Signed-off-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/md5.h

@@ -13,6 +13,8 @@
 #define MD5_H2	0x98badcfeUL
 #define MD5_H3	0x10325476UL
 
+extern const u8 md5_zero_message_hash[MD5_DIGEST_SIZE];
+
 struct md5_state {
 	u32 hash[MD5_HASH_WORDS];
 	u32 block[MD5_BLOCK_WORDS];