[ipgen] Add basic render tests
[ipgen] Add basic render tests

Add a simple pytest testing the ipgen default IP template renderer and
the parameter passing to templates.

Run with

```
pytest util/ipgen/tests/test_render.py
```

Signed-off-by: Philipp Wagner <5a4b10454c30419e54a1570be358a516ff84bb63@lowrisc.org>

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