ath10k: remove early irq handling

It's not really necessary to have a dedicated irq
handler just for the sake of catching early fw
crashes anymore. It is now safe to use one handler
even during early stages of device boot up.

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