wifi: ath12k: avoid burning CPU while waiting for firmware stats

wifi: ath12k: avoid burning CPU while waiting for firmware stats

ath12k_mac_get_fw_stats() is busy polling fw_stats_done flag while waiting
firmware finishing sending all events. This is not good as CPU is
monopolized and kept burning during the wait.

Change to the completion mechanism to fix it.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c5-00284.1-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
Tested-on: QCN9274 hw2.0 WLAN.WBE.1.5-01651-QCAHKSWPL_SILICONZ-1

Fixes: e367c924768b ("wifi: ath12k: Request vdev stats from firmware")
Reported-by: Grégoire Stein <gregoire.s93@live.fr>
Closes: https://lore.kernel.org/ath12k/AS8P190MB120575BBB25FCE697CD7D4988763A@AS8P190MB1205.EURP190.PROD.OUTLOOK.COM/
Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Tested-by: Grégoire Stein <gregoire.s93@live.fr>
Link: https://patch.msgid.link/20250612-ath12k-fw-fixes-v1-2-12f594f3b857@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>