* [X7] S.PORT devices update is now done on the bottom connector
* [X7] I introduce a PCBREV option, as previous versions didn't have this S.PORT bottom connector
* [X7] Introduce a PCBREV PIN to avoid having different 2 different firmware on X7
* Compilation fix
* [X7] PCBREV PIN was inverted
* [X7] PULL DOWN on PCBREV PIN
* S.PORT bottom connector is powered by PB.02, not PB.01
* [X7] PCBREV resistor changed
* [X7] PCBREV resistor changed