ath10k: decouple suspend code

Split up fw-related and hw-related suspension code.

Although we don't advertise WoW support to
mac80211 yet it's useful to keep the code in
suspend/resume hooks.

At this point there's no need to keep pci pm ops.
In case of WoW mac80211 calls ath10k_suspend()
which should take care of entering low-power mode.
In case WoW is not available mac80211 will go
through regular interface teradown and use start/stop.

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