This commit introduces synchronization objects and thus complete the
core API implementation. There still are some minor functions that are
not-implemented, and they will be addressed later.
Synchronization objects basics are implemented at FRES layer, then the
FRSH API uses these services to provide compliant semantic to the
application.
Implementation is done on top of FOSA mutexes and condition variables,
so that is as much portable as it is possible (we hope!).