ath10k: fix spectral scan for QCA99X0 family of chipsets

spectral_bin length (number of bins per fft sample) is usually
a value where (2^n = value), n is an integer.  All of the QCA99X0
family of chipsets seems to report a spectral_bin length of
2^n + 'm' bytes, where m = 4, 12 based on the chipset. This 'm'
bytes seems to carry some radar related info which is currently
discarded only for 'bin_len = 68' bytes. Extend this discarding of
irrelevant 'bin_len' for QCA9984, QCA9888, IPQ4019 as well by
introducing a hardware parameter 'spectral_bin_discard'. Also
for QCA988X based family of chipsets which doesn't seem to have this
issue and also for some of the hardware which I have not tested
like QCA6174/QCA9377 the existing behaviour is retained as it is.

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>