Improvements and changes in dialect conversion APIs. Type conversion
and op rewriting are now a bit more independent mechanisms. Dialect
conversion now requires a target object with the legal transformations
to be applied. Legality checks to detect illegal operations after
dialect conversion have been strengthened significantly.

MLIR LLVM commit:
commit 82d5084cf28bca7a0eebec283cdeae118dfa1d11 (HEAD)
Author: Jacques Pienaar <jpienaar@google.com>
Date:   Wed Jun 26 11:12:40 2019 -0700

    Split out TranslateClParser and add new parse method that reuses
    SourceMgr.

MLIR commit:
commit 82d5084cf28bca7a0eebec283cdeae118dfa1d11 (HEAD)
Author: Jacques Pienaar <jpienaar@google.com>
Date:   Wed Jun 26 11:12:40 2019 -0700

    Split out TranslateClParser and add new parse method that reuses
    SourceMgr.

Add DynElimination for DynReshape

use lock_guard to protect the access to m_exec_map in cpu_backend

[Fused] RNN and  GRU cells

Adjust PlaidML test tolerances

* Add LpNormalization operator along with unit tests.

* Add validation macro based on NGRAPH_CHECK.

* Add InstanceNormalization operation along with unit tests.

* Update supported ops table.

* Fix merge error.

* add send recv file

* update CMakeLists

* add to op_tbl, add to serializer

* fix bug in serializer, add MPI send recv

* not supported in MlSL

* GPU not support send recv

* add reference implementation

* send recv not supported by intel gpu

* resolve Scott's comment about construction

* style

* add comments, add to gpu not supported list

* using Output<Node> instead of shared_ptr<Node>

* add test

* disable test for MLSL

* disable test for cpu, gpu, gpuh

* add static string s_manifest = ;

* using NGRAPH_TEST so test can be disable for specific backend

* float number

* revert last change

* default

* support more data type

* change License text

* change License text

* add and ring send recv test

* add and ring send recv test

* skip send_recv_ring

* fix bug

* Run fused op decomposition recursively until no more fused ops.

* Update callback member name.

* Remove redundant conditions.

* Style apply.

fix license header again

MLIR Integration into CPU backend