[AG and RS channel tuning] Add thread work threshold to tuning models and precompute reg index in LL128 (#1641)

* Update LL128 elems per thread

* Precompute ix[g] in LL128 prim

* Make Threadthreshold part of tuning models

* Ignore channel tuning when channels are env controlled

* Tune LL128 max limit for AG

* Tune LL128 max limit for RS

* Retune AR LL128 limits due to changes

* Update CHANGELOG.md

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Co-authored-by: Jeffrey Novotny <jnovotny@amd.com>

[ROCm/rccl commit: 00c1eb098c]

projects/rccl/src/enqueue.cc

@@ -1769,6 +1769,7 @@ static ncclResult_t topoGetAlgoInfo(
     // NVLS should not need more than 16 channels to get peak BW.
     nc = comm->nvlsChannels;
   } else {
+    rcclUpdateThreadThreshold(comm, nBytes, info, threadThreshold);
     // Ring/Tree channel tuning
     while (nBytes < nc * nt * threadThreshold) {
       if (nc >= 2) nc--;