Bugfix uvma_isacov GUI=1

Created by: silabs-robin

The PR about integrating a disassembler broke runs with GUI=1. Sorry I was not aware of this until I tried GUI=1 just now.

Explanation: The use of DPI includes a shared object file (.so). By default this .so is not built and included in simulations. It is ok to run without the .so and still have references to it in the code, as long as one don't attempt to call it. Hence, I used ifdef to make such usage optional. But running in gui (xrun) treats this differently and complained about the missing symbol linkage even when it would not get called.

Solution: Ifdef the entire function that refers to the dpi function. (As opposed to ifdef on only the call to the function that refers to the dpi function).