ath6kl: Refactor ath6kl_wmi_control_rx()

Split the wmi event processing into the one which needs to be
vif specific and the reset. This is a step towards avoiding
the need for wiphy and a netdev registration before getting
any message from firmware.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>