Add DT Overlay Helper

[LivInAbsurdism]

No description provided.

[fhunleth]

Could you add a paragraph to the docs for how to use this?

The main reason is that I think that there might be a simpler way, but I'd like to iterate on how the user configures it before suggesting something that's difficult to use.

[LivInAbsurdism]

@fhunleth I can go ahead and add to the docs, but it looks like this for setup in the config

config :delux, :dt_overlays,
  overlays_path: "/data/gpio-led.dtbo",
  pins: [
    {"rgb-red0", 12},
    {"rgb-green0", 16},
    {"rgb-blue0", 21},
    {"rgb-red1", 24},
    {"rgb-green1", 25},
    {"rgb-blue1", 1}
  ]