boards/native: allow to overwrite default fs
boards/native: allow to overwrite default fs

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