Use One Slice per Basic Primitive for AllReduce, ReduceScatter, AllGather (#1681) for Single Node on Some GFX9 Systems

Using a single slice rather than the typical two provides about 5% speedup (sometimes more or less) on some GFX9 systems for single node.

src/include/device.h

@@ -288,7 +288,7 @@ struct alignas(16) ncclDevWorkColl {
   //   nChannels == (channelHi - channelLo) + 1
   uint32_t channelLo:8, channelHi:8;
   uint32_t nWarps:8;
-  uint32_t redOpArgIsPtr:1, regUsed:1, netRegUsed:1, oneNode:1, direct:2, isOneRPN:1;
+  uint32_t redOpArgIsPtr:1, regUsed:1, netRegUsed:1, oneNode:1, direct:2, isOneRPN:1, rcclUseOneSlice:1;
   uint32_t root:30, connIndex:2;
   uint16_t pivotA2ANumBiRings;
   void* recvbuff;