[MLIR] NFC : Move OpenMP dialect include to translation

[kiranchandramohan]

Summary

The OpenMP dialect include is only needed for translation
and is not required in LLVM dialect.

[ftynse]

Do we also need cmake changes to reflect this?

[kiranchandramohan]

CMake changes were made in https://reviews.llvm.org/D88351.

mlir/include/mlir/Dialect/LLVMIR/LLVMDialect.h

 // LLVM type system.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef MLIR_DIALECT_LLVMIR_LLVMDIALECT_H_
 #define MLIR_DIALECT_LLVMIR_LLVMDIALECT_H_
 
 #include "mlir/Dialect/LLVMIR/LLVMTypes.h"
-#include "mlir/Dialect/OpenMP/OpenMPDialect.h"
 #include "mlir/IR/Dialect.h"
 #include "mlir/IR/Function.h"
 #include "mlir/IR/OpDefinition.h"
 #include "mlir/IR/OpImplementation.h"
 #include "mlir/IR/TypeSupport.h"
 #include "mlir/IR/Types.h"
 #include "mlir/Interfaces/ControlFlowInterfaces.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"

mlir/lib/Target/LLVMIR/ConvertToLLVMIR.cpp

 //===- ConvertToLLVMIR.cpp - MLIR to LLVM IR conversion -------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements a translation between the MLIR LLVM dialect and LLVM IR.
 //
 //===----------------------------------------------------------------------===//
 
 #include "mlir/Target/LLVMIR.h"
 
+#include "mlir/Dialect/OpenMP/OpenMPDialect.h"
 #include "mlir/Target/LLVMIR/ModuleTranslation.h"
 #include "mlir/Translation.h"
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Verifier.h"
 #include "llvm/Support/ToolOutputFile.h"