GB minor optimizations

[gemarcano]

• Moves some pin initialization that's used by a bunch of different code-paths into one function

This is marked as a draft because I have one question. I have the following comment in the code at the moment:

 /* FIXME setup_GB sets this up too. Should this also for Datel and others?
  // Set Audio-In(PH4) to Input
  DDRH &= ~(1 << 4);
  // Enable Internal Pullup
  PORTH |= (1 << 4);
  */

The main setup_GB function also sets up Audio-In as input and enables the internal pull up, but the Datel/Pelican/Codebreaker/MonsterBrain initialization did everything else except touch this pin. Was that intentional? Or should this pin be initialized also as input for those other devices? Right now I don't see them using that pin, so it's probably just holding whatever setting was there prior.

If the answer is that there is no harm in all of them also initializing Audio-In, then I can do that and remove some extra lines from setup_GB. If not, I can remove the FIXMEs currently in the commit.