Query XGMI links from xml and adjust gfx906 channel usage (#410)

src/include/graph.h

@@ -34,6 +34,7 @@ ncclResult_t ncclTopoGetNetDev(struct ncclTopoSystem* system, int rank, struct n
 ncclResult_t ncclTopoCheckP2p(struct ncclTopoSystem* system, int64_t id1, int64_t id2, int* p2p, int *read, int* intermediateRank);
 ncclResult_t ncclTopoCheckGdr(struct ncclTopoSystem* topo, int64_t busId, int netDev, int read, int* useGdr);
 ncclResult_t ncclTopoGetIntraNetDev(struct ncclTopoSystem* system, int rank, struct ncclTopoGraph* graph, int channelId, int type, int* dev);
+ncclResult_t ncclTopoGetLinkType(struct ncclTopoSystem* system, int cudaDev1, int cudaDev2, bool* isXGMI, bool direct_only=false);
 
 // Set CPU affinity
 ncclResult_t ncclTopoSetAffinity(struct ncclTopoSystem* system, int rank);