Added "name" field to digest algorithms

src/crypto/md5.c

 }
 
 struct digest_algorithm md5_algorithm = {
+	.name		= "md5",
 	.context_len	= sizeof ( struct md5_ctx ),
 	.digest_len	= MD5_DIGEST_SIZE,
 	.init		= md5_init,

src/include/gpxe/crypto.h

  *
  */
 struct digest_algorithm {
+	/** Algorithm name */
+	const char *name;
 	/** Size of a context for this algorithm */
 	size_t context_len;
 	/** Size of a message digest for this algorithm */