wifi: ath12k: flush all packets before suspend

In order to send out all packets before going to suspend, current code
adds a 500ms delay as a workaround. It is a rough estimate and may not
work.

Fix this by checking packet counters, if counters become zero, then all
packets are sent out or dropped.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240412060620.27519-7-quic_bqiang@quicinc.com