PCI/PM: Unfold pci_platform_power_transition() in pci_power_up()

Some actions carried out by pci_platform_power_transition(() in
pci_power_up() are redundant, but before dealing with them, make
pci_power_up() call the pci_platform_power_transition() code directly
(and avoid a redundant check when pm_cap is unset while at it).

Link: https://lore.kernel.org/r/1922486.PYKUYFuaPT@kreacher


Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>