ath10k: fix scheduling while atomic config bug

Recent HTC/WMI changes introduced the bug. ath10k
was using _atomic iteration function with
sleepable functions.

mac80211 provides another iteration function but
it cannot be safely called in hw_config() callback
due to local->iflist_mtx being possibly acquired
already.

The patch uses internal vif list for iteration
purposes and removes/refactors no longer necessary
_iter functions.

Reported-By: Kalle Valo <kvalo@qca.qualcomm.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>