[mlir][nvvm] Add populate function (nfc)

[guraypp]

Summary

This work adds populate function for the nvvm to llvm conversion pattern.

mlir/include/mlir/Conversion/NVVMToLLVM/NVVMToLLVM.h

 
 class LLVMTypeConverter;
 class RewritePatternSet;
 class Pass;
 
 #define GEN_PASS_DECL_CONVERTNVVMTOLLVMPASS
 #include "mlir/Conversion/Passes.h.inc"
 
+void populateNVVMToLLVMConversionPatterns(RewritePatternSet &patterns);
+
 } // namespace mlir
 
 #endif // MLIR_CONVERSION_NVVMTOLLVM_NVVMTOLLVMPASS_H_

mlir/lib/Conversion/NVVMToLLVM/NVVMToLLVM.cpp

struct ConvertNVVMToLLVMPass
   void getDependentDialects(DialectRegistry &registry) const override {
     registry.insert<LLVM::LLVMDialect, NVVM::NVVMDialect>();
   }
 
   void runOnOperation() override {
     ConversionTarget target(getContext());
     target.addLegalDialect<::mlir::LLVM::LLVMDialect>();
     RewritePatternSet pattern(&getContext());
-    pattern.add<PtxLowering>(pattern.getContext());
+    mlir::populateNVVMToLLVMConversionPatterns(pattern);
     if (failed(
             applyPartialConversion(getOperation(), target, std::move(pattern))))
       signalPassFailure();
   }
 };
 
 } // namespace
+
+void mlir::populateNVVMToLLVMConversionPatterns(RewritePatternSet &patterns) {
+  patterns.add<PtxLowering>(patterns.getContext());
+}