Split out pci_mmcfg_check_reserved() for code reuse, which will be used
when supporting PCI host bridge hotplug.
Reviewed-by: NYinghai Lu <yinghai@kernel.org>
Signed-off-by: NJiang Liu <liuj97@gmail.com>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>