DCOs and 3.3v

A quick note on the DCO and Vdd. 

The chosen flash memory runs at max 4.6V. The Teensy 4.0 is 3.3v and not 5v compliant. That means we should probably run the DCOs at 3.3v too. However, that means the DACs must run with a 3.3v reference voltage too, as Vref cannot exceed Vdd. Thus we have to recalculate the charge voltages and possibly change the integrator cap too, to still be able to make a 5v output wave.

Also, we need to add an external resistor in parallel with R7 to get the correct calibration voltage.