drm/nouveau/acpi: fix lockup with PCIe runtime PM

Since "PCI: Add runtime PM support for PCIe ports", the parent PCIe port
can be runtime-suspended which disables power resources via ACPI. This
is incompatible with DSM, resulting in a GPU device which is still in D3
and locks up the kernel on resume (on a Clevo P651RA, GTX965M).

Mirror the behavior of Windows 8 and newer[1] (as observed via an AMLi
debugger trace) and stop using the DSM functions for D3cold when power
resources are available on the parent PCIe port.

pci_d3cold_disable() is not used because on some machines, the old DSM
method is broken. On a Lenovo T440p (GT 730M) memory and disk corruption
would occur, but that is fixed with this patch[2].

 [1]: https://msdn.microsoft.com/windows/hardware/drivers/bringup/firmware-requirements-for-d3cold
 [2]: https://github.com/Bumblebee-Project/bbswitch/issues/78#issuecomment-223549072



 v2: simply check directly for _PR3. Added affected machines.
 v3: fixed block comment coding style.

Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Acked-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>