PCI: Align hibernate poweroff flow with suspend flow for bridges

During S3 suspend, pci_pm_suspend_noirq() puts PCIe bridges with downstream
devices in a low-power state (D3hot or D3cold) when the platform allows it.
The hibernate poweroff_noirq path never did this: it only called
pci_prepare_to_sleep() for devices with no subordinate, so bridges with
active children were left in D0.

On many designs the platform firmware leaves bridges alone when the system
enters S4. This prevents being able to meet various energy certification
criteria for different parts of the world, particularly in designs with a
dGPU.

Align the hibernate flow with suspend by making pci_pm_poweroff_noirq()
use pci_pm_suspend_noirq_common() instead of the open-coded
pci_prepare_to_sleep() call.  This reuses exactly the logic the S3
suspend path uses, including the skip_bus_pm handling that keeps a
bridge in D0 when a downstream device must stay in D0 (e.g. a
configured wakeup source) and the pm_suspend_no_platform() bus-PM skip.
This alone is safe for the normal power-off-and-reboot path, since the
hibernation image is snapshotted before poweroff_noirq runs and
restoring it always goes through a full boot that re-enumerates and
retrains the PCIe links.

It isn't enough if hibernation_platform_enter() aborts after
dpm_suspend_end(PMSG_HIBERNATE) but before power-off: that recovers via
dpm_resume_start(PMSG_RESTORE) without rebooting, which calls
pci_pm_restore_noirq() instead of pci_pm_resume_noirq().  Give
pci_pm_restore_noirq() the same D3cold handling pci_pm_resume_noirq()
already has, so a bridge coming out of D3cold gets
pci_pm_bridge_power_up_actions() before its children's restore_noirq
callbacks run against a possibly untrained link.

Mirror the suspend_noirq guard for drivers as well: if a driver's
poweroff_noirq callback already left the device in a low-power state
without saving its configuration, skip pci_pm_suspend_noirq_common() and
go straight to the fixups, exactly as pci_pm_suspend_noirq() does.  This
avoids having the core call pci_save_state() on a device the driver has
already powered down, whose configuration space may no longer be
readable, which could otherwise corrupt the saved state used on a
poweroff abort.

Because the poweroff_noirq path now mirrors the already-shipping
suspend_noirq path and is guarded identically, bridges that must remain
in D0 are unaffected; only bridges that S3 suspend would have powered
down are now also powered down at hibernate.

Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Eric Naim <dnaim@cachyos.org>
Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Cc: AceLan Kao <acelan.kao@canonical.com>
Cc: Kai-Heng Feng <kaihengf@nvidia.com>
Cc: Mark Pearson <mpearson-lenovo@squebb.ca>
Cc: Denis Benato <benato.denis96@gmail.com>
Cc: Merthan Karakaş <m3rthn.k@gmail.com>
Link: https://patch.msgid.link/20260930213923.566846-3-superm1@kernel.org

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