Lib: Consider removing pindefs from lib and storing in the project

Start by locating the pindefs files, the project build directories such as app/rev2, and the main.h and driver inclusion paths. Review how HAL and CMSIS are currently stored and used across every SDR project, then discuss the impact with the listed project leads and lib maintainer. Done means an agreed dependency and pindef layout that works across the affected projects.

Describe the solution you'd like
It kinda makes no sense for us to store pin defines in a common library like this. Why don't we move the pindefs files to the project build directory? (e.g. app/rev2 for the FC). This way, we can also just include the platform-specific pindef file (for the flight computer) in main.h and not have to worry about passing it to the drivers -- it's far more platform independent.

While we're here, we also might want to consider linking CMSIS as a submodule. I manually replaced the library with a newer version a few commits ago, and we might want to consider being able to pull up the HAL and CMSIS at the same time.

Scope will affect every SDR project though, so let's think all of this through.

Describe alternatives you've considered
N/A

Additional context
N/A

Points of Contact
Design discussion for: @ETSells, @NArmistead, @266-750Balloons (rev 3, rev 2, and ground station project leads)
Lib maintainer: @ETSells