If there is no geoip extension delivered with Xampp, you cannot enable or add it on yourself. You have to ask Bitnami kindly to add that package to Xampp. Alternatively you should not use Xampp, install Apache/MySQL/PHP from your Linux repository of your distribution and then follow the installation description from
http://php.net/manual/en/geoip.installation.phpAs long as Xampp is NOT part of any linux distribution / repository, you cannot extend Xampp via standard repositories. That is a big disadvantage of using Xampp.