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!
Switch from 12-bit to 10-bit gamma to fit RGB into a uint32_t. Simplifies PIO and halves the RAM usage for F/B buffer.
Switch "flip" to *literally* swap the front and back buffers, and then asyncronously DMA the new back buffer into the front ready for the next draw.
Phil Howard