* Add fused version of Elu op

* Refactor ONNX importer prelu function to use fused op

* Style check

* Add docstrings

* Move make_constant_node to op/util

* Use make_constant_node helper

* Remove unneeded std:: prefixes

* Remove make_constant_node function, use builder::make_constant

* Remove redundant includes

* Add Elu to serializer

* Add Elu tests

* Add Elu tests to type prop

* Add Elu to list of ops unsupported on iGPU

* Add Elu to list of ops unsupported on iGPU

* Disable tests in iGPU manifest