Makefile: Ensure tools directory exists in output prior to use

With the change to make tools/version.h a file we need to make sure that
the output directory exists first otherwise we will get a build failure.

Reported-by: Peter Robinson <pbrobinson@gmail.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Fixes: 4d90f6cd98 ("tools: Avoid creating symbolic links for tools/version.h")
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Makefile

@@ -1889,6 +1889,7 @@ checkarmreloc: u-boot
 	fi
 
 tools/version.h: include/version.h
+	$(Q)mkdir -p $(dir $@)
 	$(call if_changed,copy)
 
 envtools: scripts_basic $(version_h) $(timestamp_h) tools/version.h