fix unconfigured out-of-tree building of tools

Now that the tools target requires the generated version header file, we
need to make sure that the directory it writes to exists.  In a configured
tree, this is taken care of for us.  But in an unconfigured one, the dir
does not yet exist causing a build error like so:

/bin/sh: line 5: ..../u-boot_build/include/version_autogenerated.h.tmp: No such file or directory

So create the dir for this file before we attempt to generate it.
Signed-off-by: NMike Frysinger <vapier@gentoo.org>

Makefile

@@ -533,6 +533,7 @@ tools: $(VERSION_FILE)
 endif	# config.mk
 
 $(VERSION_FILE):
+		@mkdir -p $(dir $(VERSION_FILE))
 		@( localvers='$(shell $(TOPDIR)/tools/setlocalversion $(TOPDIR))' ; \
 		   printf '#define PLAIN_VERSION "%s%s"\n' \
 			"$(U_BOOT_VERSION)" "$${localvers}" ; \