For flashing a TD1204 / TD1208 over J-link you need to use the following commands:
JLinkExe -device EFM32G210F128 -if swd -speed 1000 J-Link> loadbin xxxxx.bin,0 ... J-Link> r # reset J-Link> g # go
Total programming time is about 5 seconds. The circuit between the segger connector and the TD is the following one. (do not forget to connect VDD circuit to Segger VTref.