FFT functions and EVS Helper functions
[x] Some EVS helper functions imported. [x] Converted DoFFT and fft functions to fixed point. [x] Saturation overflow to be taken care at all calling locations of FFT.
[x] Some EVS helper functions imported. [x] Converted DoFFT and fft functions to fixed point. [x] Saturation overflow to be taken care at all calling locations of FFT.