igb: Support ports mapped in 64-bit PCI space

This patch resolves an issue with 64-bit PCI addresses being truncated
because the return values of pci_resource_start() and pci_resource_end()
were being cast to unsigned long.

Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>