PCI: Make pci_hotplug_io_size, mem_size, and bus_size private

PCI: Make pci_hotplug_io_size, mem_size, and bus_size private

These symbols:

  extern unsigned long pci_hotplug_io_size;
  extern unsigned long pci_hotplug_mem_size;
  extern unsigned long pci_hotplug_bus_size;

are only used in drivers/pci/ and do not need to be seen by the rest of the
kernel.  Move them to drivers/pci/pci.h so they're private to the PCI
subsystem.

Link: https://lore.kernel.org/r/20190724233848.73327-6-skunberg.kelsey@gmail.com
Signed-off-by: Kelsey Skunberg <skunberg.kelsey@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>