wifi: ath11k: modify the calculation of the average signal strength in station mode

Currently, the calculation of the average signal strength in station mode
is incorrect.

This is because before calculating the average signal strength, ath11k need
to determine whether the hardware and firmware support db2dbm, if the
hardware and firmware support db2dbm, do not need to add noise floor,
otherwise, need to add noise floor.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.23

Signed-off-by: Lingbo Kong <quic_lingbok@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://patch.msgid.link/20240309121129.5379-1-quic_lingbok@quicinc.com