Unify Pico and Radxa GPIO pin allocations

[swatzy]

The radxa x2l uses the pico GPIO as if it was a Raspberry pi 40 pin header (this allows for hats etc to be re-used). It has some internal wiring and this means that GPIO1 and GPIO2 have some resistors (I think they are using it as comms). To unify these 2 pieces if hardware I think we should move the Digital Inputs and Outputs down by 2.

We should also decouple the wiring from the manual and reference a hardware wiring document specific to the hardware... This would allow us to use different hardware in the future

[unifab]

@swatzy,

I believe this issue has been solved. Do you agree?
If not, what is missing?

Thanks,
Fab