wcn36xx: Add SNR reporting via get_survey()

Add support for get_survey() reporting. Current channel and noise-floor are
reported, other parameters such as scan, busy, TX and RX time are not
immediately available.

Noise is a useful metric to report, so bring it out now.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220115001646.3981501-5-bryan.odonoghue@linaro.org