cpu/nrf5x_common: use RTT based RTC implementation
cpu/nrf5x_common: use RTT based RTC implementation

OlegHahm/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,authmillenon/RIOT,OTAkeys/RIOT,jasonatran/RIOT,kYc0o/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,basilfx/RIOT,miri64/RIOT,jasonatran/RIOT,kaspar030/RIOT,ant9000/RIOT,OlegHahm/RIOT,miri64/RIOT,kaspar030/RIOT,kaspar030/RIOT,OTAkeys/RIOT,ant9000/RIOT,yogo1212/RIOT,OTAkeys/RIOT,jasonatran/RIOT,ant9000/RIOT,miri64/RIOT,authmillenon/RIOT,basilfx/RIOT,jasonatran/RIOT,yogo1212/RIOT,kYc0o/RIOT,basilfx/RIOT,ant9000/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,kaspar030/RIOT,basilfx/RIOT,kaspar030/RIOT,authmillenon/RIOT,OlegHahm/RIOT,kYc0o/RIOT,jasonatran/RIOT,yogo1212/RIOT,miri64/RIOT,authmillenon/RIOT,yogo1212/RIOT,ant9000/RIOT,basilfx/RIOT,RIOT-OS/RIOT,miri64/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,OTAkeys/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,authmillenon/RIOT