Make binaries report udev version compatibility version instead of eudev version

Software such as dracut performs a sanity check on udev by querying the
udev tools for the version. Reporting the eudev version causes this
check to fail, so we resort to reporting the udev compatibility
versionj.

Signed-off-by: Richard Yao <ryao@gentoo.org>
Ensure UDEV_VERSION is defined

Currently UDEV_VERSION is set by configure but it isn't
defined such that it could be substituted by the preprocessor.