Thanks for confirming it. We have rechecked the IAR folder and it looks like this type of register definitions is only used with 3 specific and very niche devices (RZN1D, RZN1L, RZN1S). Hence, VisualGDB does not support importing it automatically.
That said, the logic for converting SVD files into VisualGDB-specific register definitions is available here in our GitHub repository. Feel free to fork it and update it to parse the register definitions in the DDF format.
If you wish, we can also do it on our side, however, as it is unlikely to cover any mainstream devices (and help most other users), it would be subject to our consulting rate. Feel free to reach out to our sales to get a precise quote.