PCI: Move is_pciehp check out of pciehp_is_native()

PCI: Move is_pciehp check out of pciehp_is_native()

pci_bridge_d3_possible() seeks to forbid runtime power management on:

* Non Hot-Plug Capable PCIe ports which are nevertheless ACPI slots
  (recognizable as: bridge->is_hotplug_bridge && !bridge->is_pciehp)

* Hot-Plug Capable PCIe ports for which platform firmware has not granted
  PCIe Native Hot-Plug control to the operating system
  (recognizable as: bridge->is_pciehp && !pciehp_is_native(bridge))

Somewhat confusingly, the check for is_hotplug_bridge is in
pci_bridge_d3_possible(), whereas the one for is_pciehp is in
pciehp_is_native().

For clarity, check is_pciehp directly in pci_bridge_d3_possible()
(and in the other caller of pciehp_is_native(), hotplug_is_native()).

Rephrase the code comment preceding these checks to no longer mention
"System Management Mode", which is an x86 term inappropriate in generic
PCI code.  Likewise no longer mention "Thunderbolt on non-Macs", because
there is nothing Thunderbolt-specific about these checks.  It used to be
the case that non-Macs relied on the platform for Thunderbolt tunnel
management and hotplug, but they've since moved to OS-native tunnel
management (as Macs always have), hence the code comment is no longer
accurate.

There is a subsequent check for is_hotplug_bridge further down in
pci_bridge_d3_possible().  Change the check to is_pciehp because any
ports matching "bridge->is_hotplug_bridge && !bridge->is_pciehp" are
already filtered out at the top of the function.

Do the same for another check in acpi_pci_bridge_d3(), which is called
from pci_bridge_d3_possible() via platform_pci_bridge_d3().

No functional change intended.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/18b2c2110ad0f27a34b189d793310b9c4f2f24a0.1752390102.git.lukas@wunner.de