[LLVMGPU] Disable scf.forall distribution for matmulSimt (iree-org#19302

)

We are moving towards tile&fuse pipeline. `matmulSimt` pipeline is to be
deprecated. Meanwhile, all existing tests that depend on matmulsimt
pipeline shouldn't break and hence disabling the forall distribution for
the pipeline.

compiler/src/iree/compiler/Codegen/LLVMGPU/Passes.cpp

@@ -530,7 +530,7 @@ void addGPUWinogradVectorizePassPipeline(OpPassManager &funcPassManager) {
 
 void addGPUMatmulSimtPassPipeline(OpPassManager &funcPassManager,
                                   const GPUPipelineOptions &options) {
-  tileAndDistributeToWorkgroup(funcPassManager, /*useForall=*/true);
+  tileAndDistributeToWorkgroup(funcPassManager, /*useForall=*/false);
 
   funcPassManager.addPass(createConfigTrackingCanonicalizerPass());
   funcPassManager.addPass(createConfigTrackingCanonicalizerPass());