cmd:guf: Fix board detection of MC3
The board detection wasn't stable for the MC3 because it used a pin that could toggle. Reworked the detection for the MC3 to use a combination of fuses and processor type.
Dear all, On Thursday, 4th September 2025, we will test the new disaster recovery environment. A disaster recovery test will take place between 4:00 PM and 6:00 PM CEST. Please refrain from making any changes, as they will be lost. Once testing is complete, the production environment will be restored. Thank you for your understanding.
The board detection wasn't stable for the MC3 because it used a pin that could toggle. Reworked the detection for the MC3 to use a combination of fuses and processor type.