* Disable RESET keycode because of naming conflicts

* Add Pico SDK as submodule

* Add RP2040 build support to QMK

* Adjust USB endpoint structs for RP2040

* Add RP2040 bootloader and double-tap reset routine

* Add generic and pro micro RP2040 boards

* Add RP2040 onekey keyboard

* Add WS2812 PIO DMA enabled driver and documentation

Supports regular and open-drain output configuration. RP2040 GPIOs are
sadly not 5V tolerant, so this is a bit use-less or needs extra hardware
or you take the risk to fry your hardware.

* Adjust SIO Driver for RP2040

* Adjust I2C Driver for RP2040

* Adjust SPI Driver for RP2040

* Add PIO serial driver and documentation

* Add general RP2040 documentation

* Apply suggestions from code review

Co-authored-by: Nick Brassel <nick@tzarc.org>

Co-authored-by: Nick Brassel <nick@tzarc.org>