ath10k: allow explicit MSI/MSI-X disabling

This can be useful for testing and debugging.

This introduces new ath10k_pci module parameter
`irq_mode`. By default it is 0, meaning automatic
irq mode (MSI-X as long as both target HW and host
platform supports it). The parameter works on a
best effort basis.

kvalo: fix typo "ayto"

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