ath11k: Refactor spectral FFT bin size

In IPQ8074, actual FFT bin size is two bytes but hardware reports it
with extra pad size of two bytes for each FFT bin. So finally each FFT
bin advertise as four bytes size in the collected data. This FFT pad is
not advertised in IPQ6018 platform. To accommodate this different
behavior across the platforms, introduce the hw param fft_pad_sz and use
it in spectral process. Also group all the spectral params under the new
structure in hw param structure for scalable in future.

Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.4.0.1-01492-QCAHKSWPL_SILICONZ-1
Tested-on: IPQ6018 hw1.0 AHB WLAN.HK.2.4.0.1-00330-QCAHKSWPL_SILICONZ-1

Signed-off-by: Karthikeyan Periyasamy <periyasa@codeaurora.org>
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210721180809.90960-2-jouni@codeaurora.org