ath10k: fix spectral scan for QCA9984 and QCA9888 chipsets

The spectral scan has been always broken on QCA9984 and QCA9888.

Introduce a hardware parameter 'spectral_bin_offset' to resolve this issue for
QCA9984 and QCA9888 chipsets. For other chipsets, the hardware parameter
'spectral_bin_offset' is zero so that existing behaviour is retained as it is.

In QCA9984 and QCA9888 chipsets, hardware param value 'spectral_bin_discard'
is 12 bytes. This 12 bytes is derived as the sum of segment index (4 bytes),
extra bins before the actual data (4 bytes) and extra bins after the actual
data (4 bytes). Always discarding (12 bytes) happens at end of the samples and
incorrect samples got dumped, so that user can find incorrect arrangement
samples in spectral scan dump.

To fix this issue, we have to discard first 8 bytes and last 4 bytes in every
samples, so totally 12 bytes are discarded. In every sample we need to consider
the offset while taking the actual spectral data. For QCA9984, QCA9888 the
offset is 8 bytes (segment index + extra bins before actual data).

Hardware tested: QCA9984 and QCA9888
Firmware tested: 10.4-3.5.3-00053

Signed-off-by: Karthikeyan Periyasamy <periyasa@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>