wifi: ath12k: determine interface mode in _op_add_interface()

wifi: ath12k: determine interface mode in _op_add_interface()

Currently interface mode is determined each time a vdev is created.
In MLO scenario where there could be multiple vdevs this is just a
waste of time.

Move related logic into a new helper ath12k_mac_determine_vdev_type()
and call it once in ath12k_mac_op_add_interface().

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20250418-ath12k-6g-lp-vlp-v1-7-c869c86cad60@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>