ath11k: add signal report to mac80211 for QCA6390 and WCN6855

IEEE80211_HW_USES_RSS is set in ath11k, then the device uses RSS and
thus requires parallel RX which implies using per-CPU station statistics
in sta_get_last_rx_stats() of mac80211. Currently signal is only set in
ath11k_mgmt_rx_event(), and not set for RX data packet, then it show
signal as 0 for iw command easily.

Change to get signal from firmware and report to mac80211.

For QCA6390 and WCN6855, the rssi value is already in dbm unit, so
don't need to convert it again.

Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1
Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1

Signed-off-by: Wen Gong <quic_wgong@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20211216070535.31732-1-quic_wgong@quicinc.com