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.

td1204 / j-link cable