Add initial HIP_SYNC_NULL_STREAM=0 mode.

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.


[ROCm/hip commit: 27877f8854]

projects/hip/src/hip_device.cpp

@@ -298,7 +298,7 @@ hipError_t ihipGetDeviceProperties(hipDeviceProp_t* props, int device)
 hipError_t hipGetDeviceProperties(hipDeviceProp_t* props, int device)
 {
     HIP_INIT_API(props, device);
-    return ihipGetDeviceProperties(props, device);
+    return ihipLogStatus(ihipGetDeviceProperties(props, device));
 }
 
 hipError_t hipSetDeviceFlags( unsigned int flags)