PCI: save and restore PCIe 2.0 registers

PCIe 2.0 defines several new registers (Device Control 2, Link Control 2,
and Slot Control 2). Save and retore them in pci_save_pcie_state() and
pci_restore_pcie_state().

Signed-off-by: Yu Zhao <yu.zhao@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>