wifi: ath11k: fix ack signal strength calculation

Currently, the calculation of ack signal strength is incorrect.

This is because before calculating the ack 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.

Besides, the value of ack_rssi passed by firmware to ath11k should be a
signed number, so change its type to s8.

After that, "iw wlan0 station dump" show the correct ack signal strength.

Such as:
root@CDCCSTEX0799733-LIN:~# iw wlp88s0 station dump
Station 00:03:7f:12:df:df (on wlp88s0)
        inactive time:  75 ms
        rx bytes:       11599
        rx packets:     99
        tx bytes:       9029
        tx packets:     81
        tx retries:     4
        tx failed:      0
        rx drop misc:   2
        signal:         -16 dBm
        signal avg:     -24 dBm
        tx bitrate:     1560.0 MBit/s VHT-MCS 9 80MHz VHT-NSS 4
        tx duration:    9230 us
        rx bitrate:     1560.0 MBit/s VHT-MCS 9 80MHz VHT-NSS 4
        rx duration:    7201 us
        last ack signal:-23 dBm
        avg ack signal: -22 dBm

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.30
Tested-on: QCN9074 hw1.0 PCI WLAN.HK.2.7.0.1-01744-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://patch.msgid.link/20240611022550.59078-1-quic_lingbok@quicinc.com