💡[FEATURE] Support swapped DP/DM pins

[machdyne]

Describe the feature you want to implement here:

I have designed a board with DM on GPIO18 and DP on GPIO19.

Pico-PIO-USB requires that DP is always first and this is hardcoded in many places. It seems possible(?) to reverse everything in the PIO code.

On the RP2040 the USB DM pin comes before USB DP pin and I copied that convention thinking it wouldn't be a problem, maybe others will make the same assumption.

Thanks for your consideration.

[sekigon-gonnoc]

This may be accomplished by swapping the PIO instructions for low-speed and full-speed.