Adding support for Rfft2d

[kirianguiller]

Hello everyone,

In the issue Can this be done in TFLM, it was mentionned that the kernels Rfft2d and ComplexAbs were not supported by TFLM. (kernels used in tflite for the audio classification model for instance).

I wanted to know if the reason of this is a technical incompatibility or if it's possible to implement by following the step-by-step guide?

Thanks!