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/100-freebsd-compat.patch

@@ -1,6 +1,6 @@
 --- a/Makefile
 +++ b/Makefile
-@@ -584,7 +584,10 @@ UBOOTINCLUDE    := \
+@@ -634,7 +634,10 @@ UBOOTINCLUDE    := \
  		-I$(srctree)/arch/$(ARCH)/include \
  		-include $(srctree)/include/linux/kconfig.h