timex: introduce MS_PER_CS
timex: introduce MS_PER_CS

kaspar030/RIOT,kaspar030/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,ant9000/RIOT,kaspar030/RIOT,authmillenon/RIOT,miri64/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,ant9000/RIOT,kYc0o/RIOT,miri64/RIOT,kYc0o/RIOT,ant9000/RIOT,jasonatran/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,kYc0o/RIOT,kYc0o/RIOT,miri64/RIOT,ant9000/RIOT,miri64/RIOT,authmillenon/RIOT,authmillenon/RIOT,OlegHahm/RIOT,jasonatran/RIOT,OlegHahm/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT,jasonatran/RIOT,authmillenon/RIOT,ant9000/RIOT,jasonatran/RIOT