PCI: PM: Drop struct pci_platform_pm_ops

After previous changes there are no more users of struct
pci_platform_pm_ops in the tree, so drop it along with all of the
remaining related code.

No functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Ferry Toth <fntoth@gmail.com>