cpu/sam0_common/periph: add periph_rtc_rtt module to Kconfig
cpu/sam0_common/periph: add periph_rtc_rtt module to Kconfig

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