wifi: ath12k: fix ack signal strength calculation

Currently, the calculation of ack signal strength is incorrect.

This is because before calculating the ack signal strength, ath12k 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.

Besides, the value of ack_rssi passed by firmware to ath12k should be a
signed number, so change its type to s8.

This patch affects QCN9274 and WCN7850 because they have the same issue.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

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://msgid.link/20240511030917.65811-1-quic_lingbok@quicinc.com