Update codebase to include GigaDevices GD32F107 routines and Merge GD_Zombie branch

[JoNilsson]

At present the GD_Zombie branch has fallen way behind.
Creating this issue to track status and progress of efforts to incorporate the GD32F107 back into the project and prevent it from becoming Vaporware.

It was mentioned on the Dev forum in this post that "The GD based boards will not run the firmware intended for the ST boards without the modifications that Johannes (@jsphuebner) Identified."

I suggest we start by documenting what those modification suggestions proposed by @jsphuebner on the forum were here where they belong with the code and revisioning system.