This eliminates host-synchronization for null stream. Instead, the null-stream uses GPU-side events to wait for other streams. Default is OFF pending additional testing. Add enhanced null-stream test. Also refine HIP_TRACE_API.
Change-Id: Ied0aa6055673c687071b4a579aecd17f0f3f09ce
Change-Id: I7de3fc32f13182b5c41a4e44147b642ba15e8636
Change-Id: I87ff9b3f1203d0909f998c96c839f7b321fc3f09