ath10k: fix core PCI suspend when WoWLAN is supported but disabled

For devices where the FW supports WoWLAN but user-space has not
configured it, we don't do any PCI-specific suspend/resume operations,
because mac80211 doesn't call drv_suspend() when !wowlan. This has
particularly bad effects for some platforms, because we don't stop the
power-save timer, and if this timer goes off after the PCI controller
has suspended the link, Bad Things will happen.

Commit 32faa3f0 ("ath10k: add the PCI PM core suspend/resume ops")
got some of this right, in that it understood there was a problem on
non-WoWLAN firmware. But it forgot the $subject case.

Fix this by moving all the PCI driver suspend/resume logic exclusively
into the driver PM hooks. This shouldn't affect WoWLAN support much
(this just gets executed later on).

I would just as well kill the entirety of ath10k_hif_suspend(), as it's
not even implemented on the USB or SDIO drivers. I expect that we don't
need the callback, except to return "supported" (i.e., 0) or "not
supported" (i.e., -EOPNOTSUPP).

Fixes: 32faa3f0 ("ath10k: add the PCI PM core suspend/resume ops")
Fixes: 77258d40 ("ath10k: enable pci soc powersaving")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Cc: Ryan Hsu <ryanhsu@qti.qualcomm.com>
Cc: Kalle Valo <kvalo@qca.qualcomm.com>
Cc: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>