PCI: Make saved capability state private to core

PCI: Make saved capability state private to core

Interfaces and structs for saving and restoring PCI Capability state were
declared in include/linux/pci.h, but aren't needed outside drivers/pci/.

Move these to drivers/pci/pci.h:

  struct pci_cap_saved_data
  struct pci_cap_saved_state
  void pci_allocate_cap_save_buffers()
  void pci_free_cap_save_buffers()
  int pci_add_cap_save_buffer()
  int pci_add_ext_cap_save_buffer()
  struct pci_cap_saved_state *pci_find_saved_cap()
  struct pci_cap_saved_state *pci_find_saved_ext_cap()

Link: https://lore.kernel.org/r/20210802221728.1469304-1-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>