Enable HSwish - ngraph op, fusion/decomposition and reference implementation (#1770)
* Add HSwish operator to nGraph
* Add HSwishFusion transformation
* Update check_constant function
* Add reference implementation for HSwish
* Enable reference implemenation in HSwish evaluate
* Add op_eval test
* HSwish fusion transformation test
* Add HSwishFusionWithoutRelu transformation
* Add more hswish fusion tests
* Register HSwishFusion pass in common_optimizations
* Update HSwish reference implementation
* Add HSwishFusion with Relu and Multiply
* Add HSwishDecomposition transformation pass
* Add HSwishDecomposition test
* Add HSwish op to ngraph python API
* Update HSwish fusion transformations
* Remove HSwishFusion from common optimizations
* Update hswish python API
* Add bf16 to evaluate hswish
* Update hswish python API
* Move hswish reference implementation
* UnaryElementwiseArithmetic inheritance
* Enable HSwish callback for clDNN
* Register HSwishDecomposition pass in ConvertOpSet1ToLegacy
* Enable HSwishFusion pass in common optimizations
* Use NGRAPH_RTTI_DECLARATION
* Moved python hswish test to the test_ops_unary