The expandable GPIO API requires the comparison of structured GPIO types. This means that inline functions must be used instead of direct comparisons. For the migration process, tests must first be changed so that they use the inline comparison functions.
Replace direct accesses to sched_active_thread and sched_active_pid with
the helper functions thread_getpid() and thread_get_active(). This serves
two purposes:
1. It makes accidental writes to those variable from outside core less likely.
2. Casting off the volatile qualifier is now well contained to those two
functions
