Makefile: move $(VERSION_FILE) rule out of ifeq configured

mkimage relies on autogenerated version so we need to move
$(VERSION_FILE) rule out of ifeq and make tools rule depend on it to be
able to run 'make tools' from the unconfigured tree.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>