[FEATURE] Unit tests for the VIDC

[RichardBrown384]

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