ath10k: re-add support for early fw indication

It's possible for FW to panic during early boot.

The patch re-introduces support to detect and
print those crashes.

This introduces an additional irq handler that is
set for the duration of early boot and shutdown.
The handler is then overriden with regular
handlers upon hif start().

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