[GNA] Support in GNA plugin for power layer with non-1 exponents (#997)

[GNA] Support in GNA plugin for power layer with non-1 exponents (#997)

* added support for power layer with non-1 exponents to GNA plugin

* reverted a change caused by merge issue

* fixes for review comments (typo fix - lrelu instead of leru, unnamed structure instead of of named one in union with arguments of activation function, name fix - input instead of inputs),

scale-shift implementation based on affine layer instead of PWL,

* fixed code style

* fixes for coding style in scale_factor_calc.hpp

* added domain for power function

* fixed review comment - power function specific methods

* added check if dynamic casting was successful

* removed I16 as it is not supported by ngraph

* fixed initialization per review comment