wifi: ath12k: remove redundant logic for initializing arvif

wifi: ath12k: remove redundant logic for initializing arvif

The current logic for initializing arvif is present in both the add
interface operation callback and ath12k_mac_assign_link_vif(). The former
handles deflink initialization, while the latter is responsible for other
links. This redundancy could be avoided by using a common helper function.

Hence, add a new helper ath12k_mac_init_arvif() which initializes a
given arvif.

Since synchronizing rcu is not required after adding a rcu pointer, remove
that now.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00173-QCAHKSWPL_SILICONZ-1
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00130-QCAHKSWPL_SILICONZ-1.97421.5 # Nicolas Escande

Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Signed-off-by: Aditya Kumar Singh <aditya.kumar.singh@oss.qualcomm.com>
Tested-by: Nicolas Escande <nico.escande@gmail.com>
Link: https://patch.msgid.link/20250204-unlink_link_arvif_from_chanctx-v2-4-764fb5973c1a@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>