Add possibility to use library with different DMA_IRQ

[negis02]

Thanks for grate library.
I hawed a issue to get work this library together with Adafruit_NeoPXL8, because both libraries using same DMA_IRQ.
so i edit DmxInput.cpp file in Pico-DMX:

dma_hw->ints0 = 1u << i;
dma_channel_set_irq0_enabled(_dma_chan, true);
irq_set_exclusive_handler(DMA_IRQ_0, dmxinput_dma_handler);
irq_set_enabled(DMA_IRQ_0, true);

to

dma_hw->ints1 = 1u << i;
dma_channel_set_irq1_enabled(_dma_chan, true);
irq_set_exclusive_handler(DMA_IRQ_1, dmxinput_dma_handler);
irq_set_enabled(DMA_IRQ_1, true);

Now I'm able to control animation patterns of 4000 WS2812 pixels at 35FPS (4 strips 1000LED length) by DMX signal in my project.

[PaintYourDragon]

This is semi-addressed in NeoPXL8 1.2.3. Partly by changing that code to DMA IRQ 1 (should then play nice with this library), but also by using a shared (rather than exclusive) IRQ handler (should play nice with other libraries if they’re using shared handlers). I’d recommend making a similar change in Pico-DMX for broadest compatibility.

Fairly straightforward, can see this in github.com/adafruit/Adafruit_NeoPXL8
Adafruit_NeoPXL8.cpp around lines 140 and 371