gzip/zlib: make features optional

If you really want to slim down U-Boot and you would rather use a higher
compression scheme (like LZMA), it'd be nice to disable gzip/zlib since
these code bases take up a significant amount of space.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/config_defaults.h b/include/config_defaults.h
index 08b6ede..0337163 100644
--- a/include/config_defaults.h
+++ b/include/config_defaults.h
@@ -14,4 +14,7 @@
 #define CONFIG_BOOTM_NETBSD 1
 #define CONFIG_BOOTM_RTEMS 1
 
+#define CONFIG_GZIP 1
+#define CONFIG_ZLIB 1
+
 #endif