Associated change is to optimize event recording so it uses
agent-scope releaes (since it was only using system-scope release
to support non-coherent host mem).
Flags and environment variables exist to obtain previous behavior
if desired. Options are documented in new performance guide.
[ROCm/hip commit: 8b8e97ff28]
Yaxun (Sam) Liu
Rahul Garg
Ben Sander