ACPI / hotplug / PCI: Use cached copy of PCI_EXP_SLTCAP_HPC bit

We cache the PCI_EXP_SLTCAP_HPC bit in pci_dev->is_hotplug_bridge on device
probe, so there's no need to read it again when adding the ACPI hotplug
context.

Here's the call chain to prove that no ordering issue is introduced:

pci_scan_child_bus [drivers/pci/probe.c]
  pci_scan_slot
    pci_scan_single_device
      pci_scan_device
        pci_setup_device
          set_pcie_hotplug_bridge
            [is_hotplug_bridge bit is set here]
  pci_scan_bridge
    pci_add_new_bus
      pci_alloc_child_bus
        pcibios_add_bus  [arch/(x86|arm64|ia64)/...]
          acpi_pci_add_bus [drivers/pci/pci-acpi.c]
            acpiphp_enumerate_slots [drivers/pci/hotplug/acpiphp_glue.c]
              acpiphp_add_context
                device_is_managed_by_native_pciehp
                  [is_hotplug_bridge bit is queried here]

No functional change intended.
Tested-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: NLukas Wunner <lukas@wunner.de>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/pci/hotplug/acpiphp_glue.c

@@ -225,14 +225,11 @@ static void acpiphp_post_dock_fixup(struct acpi_device *adev)
 /* Check whether the PCI device is managed by native PCIe hotplug driver */
 static bool device_is_managed_by_native_pciehp(struct pci_dev *pdev)
 {
-	u32 reg32;
 	acpi_handle tmp;
 	struct acpi_pci_root *root;
 
 	/* Check whether the PCIe port supports native PCIe hotplug */
-	if (pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, &reg32))
-		return false;
-	if (!(reg32 & PCI_EXP_SLTCAP_HPC))
+	if (!pdev->is_hotplug_bridge)
 		return false;
 
 	/*