ath11k: support avg signal in station dump

Currently mac80211 doesn't calculate average signal when RSS(Receive side
scaling) is enabled from the driver, so average signal isn't printed in
the station dump. To address this issue, calculate the average signal
from RSSI within driver and display in the station dump.

Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.5.0.1-01208-QCAHKSWPL_SILICONZ-1

Signed-off-by: Thiraviyam Mariyappan <quic_tmariyap@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/1652965061-30457-1-git-send-email-quic_tmariyap@quicinc.com