Add pico-sdk & libhal-rp2040 library

[kammce]

The pico-sdk code is BSD-3 which is compatible with libhal's Apache 2 license. We should make a 3P library for the pico-sdk, have libhal-rp2040 require it and use it to implement the libhal interfaces. Unlike NXP and STM software with restrictive licenses, we can simply borrow code from the pico sdk. Note that I strongly feel that the libhal team should implement drivers for SDKs with problematic code. But if the software is shown to work well and is stable, then we should opt for the faster option of utilizing the software that already exists.

Note about ST's license. I plan to use the libhal-stm32f1 and any others that we support with copycat hardware from gigadevice to the others. From ARM to RISC-V. The drivers work as expected, but need to be mapped to different locations. If we had used the original st software, we wouldn't be able to do this and their SDK wouldn't be designed in a way that makes it easy for us to port to the copy cats.