modules: Refactor pw_board_led This CL splits the LED code between //drivers:system and a more abstract //modules/indicators. This allows for better dependency injection, and encapsulates the facade in a single directory. Change-Id: Ic0dda16fbdb78bca51580e1dc06c1344e060d45d Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/showcase/rp2/+/218835 Reviewed-by: Alexei Frolov <frolv@google.com> Commit-Queue: Aaron Green <aarongreen@google.com> Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>