PCI: pciehp: Rename host->native_hotplug to host->native_pcie_hotplug

Rename host->native_hotplug to host->native_pcie_hotplug to make room for a
similar flag for SHPC hotplug.

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
[bhelgaas: split to separate patch]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>