PCI: Disable D3cold on Asus B1400 PCI-NVMe bridge

PCI: Disable D3cold on Asus B1400 PCI-NVMe bridge

The Asus B1400 with original shipped firmware versions and VMD disabled
cannot resume from suspend: the NVMe device becomes unresponsive and
inaccessible.

This appears to be an untested D3cold transition by the vendor; Intel
socwatch shows that Windows leaves the NVMe device and parent bridge in D0
during suspend, even though these firmware versions have StorageD3Enable=1.

The NVMe device and parent PCI bridge both share the same "PXP" ACPI power
resource, which gets turned off as both devices are put into D3cold during
suspend. The _OFF() method calls DL23() which sets a L23E bit at offset
0xe2 into the PCI configuration space for this root port.  This is the
specific write that the _ON() routine is unable to recover from. This
register is not documented in the public chipset datasheet.

Disallow D3cold on the PCI bridge to enable successful suspend/resume.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215742
Link: https://lore.kernel.org/r/20240228075316.7404-1-drake@endlessos.org
Signed-off-by: Daniel Drake <drake@endlessos.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Jian-Hong Pan <jhp@endlessos.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>