omx: Implement new approach for locking that should solve all deadlocks on RPi

omx: Implement new approach for locking that should solve all deadlocks on RPi

No mutex is locked while calling any OpenMAX functions anymore
and everything from the OpenMAX callbacks is inserted into a message
queue and handled from outside the callbacks.

Also there's only a single mutex and condition variable per component
now for handling anything from OpenMAX callbacks and a single mutex
for keeping our component/port state sane.