Enable misra c2012 8.7

[dzid26]

Bounty #1794
I picked up after #1830., rebased on the head and made minor fixes.

[dzid26]

The PR fixes rule 8.7, but this rule seems pointless for the "hierarchical headers" architecture of Panda codebase

In the context of rule 8.7, using static is meant to reduce visibility within a given translation unit.
But Panda has only one translation unit (main.c) as it doesn't use the common source/header pair architecture, so it requires static in front of every function and object defined externally.

Cppcheck 2.13 doesn't detect all of them as violations (maybe it gets confused by the hierarchical includes). cppcheck 2.14 detects more, but not all off them. For example it detects dos_check_ignition() but not dos_read_som_gpio()

There is one benefit of solving 8.7 that I can see. - It allows to detect 8.9 violations. 8.9 is about narrowing scope of the objects - which is good. It sometimes makes the code look more messy though, when constants need to be moved from top of the file to a function body.