PCI/ASPM: Move pci_configure_ltr() to aspm.c

PCI/ASPM: Move pci_configure_ltr() to aspm.c

The Latency Tolerance Reporting (LTR) mechanism supports the ASPM L1.2
state and is only configured when CONFIG_PCIEASPM is set.

Move pci_configure_ltr() and pci_bridge_reconfigure_ltr() into aspm.c since
they only build when CONFIG_PCIEASPM is set.  No functional change
intended.

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20240128233212.1139663-2-david.e.box@linux.intel.com
[bhelgaas: commit log, split build change from function moves]
Link: https://lore.kernel.org/r/20240223205851.114931-2-helgaas@kernel.org
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>