[FEATURE] Unit tests for the VIDC

**Is your feature request related to a problem? Please describe.**
The VIDC has no tests

**Describe the solution you'd like**
The VIDC should be tested with tests for
- [ ] Register writes
- [ ] Colour mapping
- [ ] Timing aspects
- [ ] DMA request timing
- [ ] Edge cases for register values (0 etc)

**Describe alternatives you've considered**
None

**Additional context**
None
