* [MLIR] Fix naming convention in MLIR files

Add naming convention note per file to state which files should use
nGraph naming convention and which MLIR naming convention and align
naming convention in those files with such a note.

* Remove m-prefix

* [MLIR] Replace MatmulBiasOp with DotOp

We disable CPUFusion if MLIR is enabled to avoid CPU specific ops to be
introduced for now.

* Move dialect and types to mlir namespace

* PR fixes and some cleanup

* Merge fix

* Initial td file. Cmake changes

* Move all ops to .td file.

* Added few more opcodes to show-case. Fixed PR feedback

* Remove NG_ prefix of opcode records. Some fixes

* Added some doc

*  Adding back NG prefix

* Bug fix in MLIR gen

* Use NGRAPH export macros instead of CPU

* Move code to ngmlir namespace

* Move MLIR to src/contrib/mlir

* Create MLIR as cmake external project. Clone and build via ngraph cmake

* Moved code and enabled compilation. Need to clone and build MLIR/LLVM during cmake step, so find_package can work

* clone and build llvm/mlir during configuration. Compiles now. Needs more testing

* Force DEX only if MLIR is ON

* Remove extra cmake file. Style-apply

* Remove redundant files in cpu/mlir

* Update CODEOWNERS. Check for ninja and fail if not found

* Fixing post merge issues

* Implements a simple memory manager that just does malloc for now. Pointers are freed during cleanup.
* Enable JIT call-back to memory manager to allocate temps.
* Memory manager pointer is passed to the JIT'ed code upon invocation. That makes the code re-entrant from different threads in case the code is shared among identical sub-graphs that are executed in parallel.

The following test should work now:
NGRAPH_MLIR_DUMP_ALL=1 NGRAPH_MLIR=1 test/unit-test '--gtest_filter=CPU.dot2d'

* Link MLIR static libs to cpu backend

* Use LLVMConfig.cmake

* Initial commit. Link fails with undefined reference to typeinfo for mlir::Dialect

* Added AddOp

* initial compiler class

* Initialize module/function, and map tensors to arguments

* Code compiles. Moved MLIR building to correct DEX handler

* NGDialect code-gen working

* Use vector instead of sets for i/o tensors. Use functor in executor

* Misc fixes

* style-apply

* WIP: Adding support for dialect lowering.

* WIP: Lowered to affine. Crash on constant ops have side effects in Constant Folding

* Fixed missing whole package linkage.

* Removed fake instruction and update func type

*  Enable lowering to LLVM dialect and IR

* Made loop nest builder handle any rank

* Fixes per PR feedback. Major ones:
- Removed ngdialect namespace
- renamed dialect classes to start with NG prefixwq:w

* Add unreachable assert

* Add reading of LLVM options from an env var MLIR_LLVM_OPTIONS (#5)