pico-sdk partial tree

https://github.com/raspberrypi/pico-sdk

This is just a partial copy of the pico-sdk repository to reduce repository size. The following paths are extracted:

• LICENSE.TXT
• src/rp2040/hardware_regs/include
• src/rp2040/hardware_structs/include
• src/rp2_common/cmsis/stub/CMSIS/Device/RaspberryPi/RP2040/Include
• tools/pioasm/

Boot2 variants are built from src/rp2_common/boot_stage2. The stand-alone pioasm can be compiled as such:

mkdir -p pioasm/build && cd pioasm/build
cmake .. && make

This repository is updated periodically by Github Actions.