Introduce multi-rank support per device.

This is a single commit of the source code changes required to
introduce support for multiple ranks per device.
A new interface (ncclCommRankInitMulti) has to be used to make use of
this new feature.


[ROCm/rccl commit: 0336ffdf70]

projects/rccl/src/include/comm.h

@@ -112,6 +112,7 @@ struct ncclComm {
   int64_t busId;   // my PCI bus ID in int format
   cpu_set_t cpuAffinity; // CPU affinity of the GPU
   int WarpSize;
+  int virtualId;
 
   int node;
   int nNodes;