PCI/PM: Avoid exporting __pci_complete_power_transition()

Notice that radeon_set_suspend(), which is the only caller of
__pci_complete_power_transition() outside of pci.c, really only
cares about the pci_platform_power_transition() invoked by it,
so export the latter instead of it, update the radeon driver to
call pci_platform_power_transition() directly and make
__pci_complete_power_transition() static.

Code rearrangement, no intentional functional impact.

Link: https://lore.kernel.org/r/1731661.ykamz2Tiuf@kreacher


Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>