Defensively tear down DMA/PIO so it's in a known good state upon (soft)reset.
Issue was a race condition with DMA interrupts firing and not being achknowledged, leaving a stuck raised IRQ.
The blocking wait for DMA transactions also exacerbated this, turning a borken DMA interrupt and blank screen into an unrecoverable hardlock.
...not that the blank screen was recoverable without a soft reset anyway!
The FM6126A register write was causing some weirdness on soft reset where the pin state wasn't predictable.
Have twiddled some pins at startup to ensure everything works as expected.
Add set_hsv and set_all_hsv (since setting individual pixels with hsv is S L O W)
Made "flip()" blocking, it was easy to accidentally get a little tearing.
Switch MicroPython HUB75 driver over to DMA/PIO.
TODO:
* Move this into drivers for C++ use too
* Fix hitting "Stop" in Thonny causing rows to stick on the display (this is bad, and should not happen)
* Fix "Stop -> Start" in Thonny causing weird display issues (it's not memory offets, maybe DMA/PIO issues?)
Phil Howard