makefiles/riotboot: ensure BUILDDEPS are built before riotboot targets
makefiles/riotboot: ensure BUILDDEPS are built before riotboot targets

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