Add special handling of gfx940 (#976)

* Add special handling of gfx940

* Update ring base

[ROCm/rccl commit: 50b2dd9fd7]

projects/rccl/tools/topo_expl/topo_expl.cpp

@@ -154,6 +154,8 @@ NodeModelDesc model_descs[] = {
   {1, "topo_8p_940.xml",        "Single node gfx940 8P"},
   {2, "topo_4p_940.xml",        "2 nodes gfx940 4P"},
   {4, "topo_8p_940.xml",        "4 nodes gfx940 8P"},
+  {1, "topo_8p_940vm.xml",      "single node gfx940 VM"},
+  {2, "topo_8p_940vm.xml",      "2 nodes gfx940 VM"},
 };
 
 NCCL_PARAM(MaxCTAs, "MAX_CTAS", MAXCHANNELS);