makefiles/boards/sam0.inc.mk: dap: use OpenOCD for debugging
makefiles/boards/sam0.inc.mk: dap: use OpenOCD for debugging

ebdg can only be used for flashing, we still have to use OpenOCD for
debugging.

fixes #14328

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