cpu/stm32/kconfig: create family directory if not exist
cpu/stm32/kconfig: create family directory if not exist

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