PCI/ASPM: Save L1 PM Substates Capability for suspend/resume

PCI/ASPM: Save L1 PM Substates Capability for suspend/resume

Previously the L1 PM Substates Control Registers (CTL1 and CTL2) weren't
saved and restored during suspend/resume leading to the L1 PM Substates
configuration being lost post-resume.

Save the L1 PM Substates Control Registers so that the configuration is
retained post-resume.

[bhelgaas: drop pci_is_pcie() testing; we can rely on pci_configure_ltr()
having already done that]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vidya Sagar <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>