wifi: ath12k: enable 802.11 power save mode in station mode

To reduce power consumption enable 802.11 power save mode in
station mode. This allows both radio and CPU to sleep more.

Only enable the mode on WCN7850, other chips don't support it
for now.

To test that power save mode is running, run below command and
check there is no NULL Data frame seen by a sniffer:
        iw dev <inf> set power_save off

And run below command, then check there is a NULL Data frame
in sniffer:
        iw dev <inf> set power_save on

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

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240201035830.2534-1-quic_bqiang@quicinc.com