Force EEM SOURCE

[nkrackow]

Find out what is needed here. Maybe just setting some IOs.

[jordens]

Match EEM behavior and support from stabilizer.
Refactor common code.
https://github.com/quartiq/stabilizer/blob/6a61600fc6f024b92dfad67332b3fb8a6c34f8eb/src/hardware/setup.rs#L1073-L1154