Audit RP2040 config_autogen.h and other compilation settings

[vkottler]

See this comment: #11 (comment)

I don't know if this is worth doing until we actually find something that needs to be addressed, but it's an open item either way.

[vkottler]

What we really need to do here is just dial back as much as possible on "high-level" pico-sdk code.

Almost every bit of this code is littered with preprocessor conditional logic. The hardware and struct layer, plus the generic hardware HAL interfaces are pretty great though.