ubootTools: set CONFIG_ARCH_MVEBU=y

u-boot only builds some architecture-specific tools, if this
architecture is selected in configuration. So a 'allnoconfig' won't
include them.

As they are pretty useful however, we'd like to have them in ubootTools.
This can be accomplished by enabling CONFIG_KIRKWOOD=y and possibly
more later.

pkgs/misc/uboot/default.nix

···
     buildFlags = "tools NO_SDL=1";
     dontStrip = false;
     targetPlatforms = stdenv.lib.platforms.linux;
-    filesToInstall = ["tools/dumpimage" "tools/mkenvimage" "tools/mkimage"];
+    # build tools/kwboot
+    extraMakeFlags = [ "CONFIG_KIRKWOOD=y" ];
+    filesToInstall = [
+      "tools/dumpimage"
+      "tools/fdtgrep"
+      "tools/kwboot"
+      "tools/mkenvimage"
+      "tools/mkimage"
+    ];
   };
 
   ubootA20OlinuxinoLime = buildUBoot rec {