[gfx950] Make bypassing __threadfence the default for multinode. (#1947)

* Gate based on ROCM version, safe for ROCm 7.0.2 and beyond.
* Updates naming to gfx9CheapFenceOff since we use this for gfx942 and gfx950.  Thanks Nilesh.
* Add info logging statement to NCCL_INIT to print whether enabled when INFO logging is enabled.

[ROCm/rccl commit: c70f5b4621]

projects/rccl/src/device/prims_simple.h

@@ -875,7 +875,7 @@ public:
       patBarrier();
     }
     if(collWork){
-      skip_fence = !collWork -> gfx942CheapFenceOff;
+      skip_fence = !collWork -> gfx9CheapFenceOff;
     }
   }