embassy-rp: Add support for color order to Pio::Ws2812

[bobdoah]

This adds support for setting a color order when using the Pio::Ws2812 lib. I am using a WS2812 strip that uses RGB color order instead of the more typical GRB order, and this felt like a nice addition.

The default GRB usage remains identical and the example in examples/rp235x/src/bin/pio_ws2812.rs works unchanged. To use with a specified color order, you need to use a type annotation:

let program = PioWs2812Program::new(&mut common);
let mut ws2812: PioWs2812<'_, _, 0, 50, Rgb> =
     PioWs2812::with_color_order(&mut common, sm0, p.DMA_CH0, p.PIN_15, &program);

[lulf]

thanks!