igc: Remove unneeded PCI bus defines

PCIe device control 2 defines does not use internally.
This patch comes to clean up those.

Signed-off-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>