lib: zlib: include deflate into zlib build

Add a new config CONFIG_GZIP_ENABLED, if enabled, the uboot bin would
include zlib's deflate method which could be used for compressing.

Signed-off-by: Lei Wen <leiwen@marvell.com>
diff --git a/lib/zlib/zlib.c b/lib/zlib/zlib.c
index 230d0df..7e15702 100644
--- a/lib/zlib/zlib.c
+++ b/lib/zlib/zlib.c
@@ -12,6 +12,14 @@
  * - added inflateIncomp
  */
 
+#include <common.h>
+
+#ifdef CONFIG_GZIP_COMPRESSED
+#define NO_DUMMY_DECL
+#include "deflate.c"
+#include "trees.c"
+#endif
+
 #include "zutil.h"
 #include "inftrees.h"
 #include "inflate.h"