PCI/portdrv: Rename and reverse sense of pcie_ports_auto

The platform may restrict the OS's use of PCIe services, e.g., via the ACPI
_OSC method.  The user may use "pcie_ports=native" to force the port driver
to use PCIe services even if the platform asked us not to.

The "pcie_ports=native" parameter determines the setting of
pcie_ports_auto.  Rename this to pcie_ports_native and reverse the
sense to simplify the code.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>