wifi: ath12k: Enable IMPS for WCN7850

To reduce power consumption, change idle_ps to true to enable
Idle Mode Power Save (IMPS) for WCN7850.

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>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20230317062533.18240-1-quic_bqiang@quicinc.com