wifi: ath12k: support suspend/resume

wifi: ath12k: support suspend/resume

Now that all infrastructure is in place and ath12k is fixed to handle all the
corner cases, power down the ath12k firmware during suspend and power it back
up during resume.

For suspend, two conditions needs to be satisfied:

1. since MHI channel unprepare would be done in late suspend stage,
   ath12k needs to get all QMI-dependent things done before that stage.
2. and because unprepare MHI channels requires a working MHI stack,
   ath12k is not allowed to call mhi_power_down() until that finishes.

So the original suspend callback is separated into two parts: the first part
handles all QMI-dependent things in suspend callback; while the second part
powers down MHI in suspend_late callback. This is valid because kernel calls
ath12k's suspend callback before calling all suspend_late callbacks, making
the first condition satisfied. And because MHI devices are children of ath12k
device (ab->dev), kernel guarantees that ath12k's suspend_late callback is
called after QRTR's suspend_late callback, this satisfies the second condition.

Above analysis also applies to resume process. so the original resume
callback is separated into two parts: the first part powers up MHI stack
in resume_early callback, this guarantees MHI stack is working when
QRTR tries to prepare MHI channels (kernel calls QRTR's resume_early callback
after ath12k's resume_early callback, due to the child-father relationship);
the second part waits for the completion of restart, which would succeed
since MHI channels are ready for use by QMI.

Another notable change is in power down path, we tell mhi_power_down() to not
to destroy MHI devices, making it possible for QRTR to help unprepare/prepare
MHI channels, and finally get us rid of the potential probe-defer issue when
resume.

Also change related code due to interface changes.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0-03427-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1.15378.4
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240412060620.27519-10-quic_bqiang@quicinc.com