Add support for the RGB LED on the board sold on Aliexpress

[wired-filipino-owl]

I tried to mirror the LED colors of the Zero board. I based this off of 1.0.2, as 1.0.3 doesn't seem to work yet.

See #68 for information about the Aliexpress (BitfunX) board. It would be easy enough to make a test rig with a regular off-the-shelf Pico, and just hook up LEDs to GPIO 23 and 24.

I tested the firmware with my Aliexpress PicoMemcard and it seems to work fine, but more testing is welcome.