[mlir] Update doc to omit the usage of LLVMIntegerType

[Lewuathe]

Summary

Since the LLVMIntegerType was replaced with build-in integer type, the usage in the tutorial should be also updated accordingly.
We need to update chapter 6 for Toy tutorial specifically.

See: https://reviews.llvm.org/D94178

[Lewuathe]

@rriddle Thank you! Since I do not have write access, could you land this change in the repo on behalf of me?

[ftynse]

Please consider avoiding "advanced" markdown features in the commit messages, a lot of people look at them in the terminal and it may be hard to parse

[url | long description that
spans several lines]

mentally. Small things like underscores and asterisks for highlighting are fine IMO.

mlir/docs/Tutorials/Toy/Ch-6.md

static FlatSymbolRefAttr getOrInsertPrintf(PatternRewriter &rewriter,
                                            ModuleOp module,
                                            LLVM::LLVMDialect *llvmDialect) {
   auto *context = module.getContext();
   if (module.lookupSymbol<LLVM::LLVMFuncOp>("printf"))
     return SymbolRefAttr::get("printf", context);
 
   // Create a function declaration for printf, the signature is:
   //   * `i32 (i8*, ...)`
-  auto llvmI32Ty = LLVM::LLVMIntegerType::get(context, 32);
+  auto llvmI32Ty = IntegerType::get(context, 32);
   auto llvmI8PtrTy =
-      LLVM::LLVMPointerType::get(LLVM::LLVMIntegerType::get(context, 8));
+      LLVM::LLVMPointerType::get(IntegerType::get(context, 8));
   auto llvmFnType = LLVM::LLVMFunctionType::get(llvmI32Ty, llvmI8PtrTy,
                                                 /*isVarArg=*/true);
 
   // Insert the printf function into the body of the parent module.
   PatternRewriter::InsertionGuard insertGuard(rewriter);
   rewriter.setInsertionPointToStart(module.getBody());
   rewriter.create<LLVM::LLVMFuncOp>(module.getLoc(), "printf", llvmFnType);
   return SymbolRefAttr::get("printf", context);