tools/mkimage: update to version 2018.03

This activates support for fit images and some other new mkimage
features. Some of the patches were applied upstream and could be
removed.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

tools/mkimage/patches/050-image_h_portability.patch

@@ -8,7 +8,7 @@
  
  /* Define this to avoid #ifdefs later on */
  struct lmb;
-@@ -258,13 +257,13 @@ struct lmb;
+@@ -308,13 +307,13 @@ enum {
   * all data in network byte order (aka natural aka bigendian).
   */
  typedef struct image_header {