wifi: ath12k: report station mode per-chain signal strength

wifi: ath12k: report station mode per-chain signal strength

Currently, command “iw wlan0 station dump” does not show per-chain signal
strength.

This is because ath12k does not handle the num_per_chain_rssi and
rssi_avg_beacon reported by firmware to ath12k.

To address this, update ath12k to send WMI_REQUEST_STATS_CMDID with the
flag WMI_REQUEST_RSSI_PER_CHAIN_STAT to the firmware. Then, add logic to
handle num_per_chain_rssi and rssi_avg_beacon in the
ath12k_wmi_tlv_fw_stats_parse(), and assign the resulting per-chain signal
strength to the chain_signal of struct station_info.

After that, "iw dev xxx station dump" shows the correct per-chain signal
strength.
Such as:

Station AA:BB:CC:DD:EE:FF (on wlan0)
        inactive time:  212 ms
        rx bytes:       10398
        rx packets:     64
        tx bytes:       4362
        tx packets:     33
        tx retries:     49
        tx failed:      0
        beacon loss:    0
        beacon rx:      14
        rx drop misc:   16
        signal:         -45 [-51, -46] dBm
        beacon signal avg:      -44 dBm

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4

Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219751
Signed-off-by: Lingbo Kong <lingbo.kong@oss.qualcomm.com>
Reviewed-by: Baochen Qiang <baochen.qiang@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250812030044.688-1-quic_lingbok@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>