PCI/PM: Split pci_raw_set_power_state()

PCI/PM: Split pci_raw_set_power_state()

The transitions from low-power states to D0 and the other way around
are unnecessarily tangled in pci_raw_set_power_state() which makes it
rather hard to follow.

Moreover, the only caller of pci_raw_set_power_state() passing PCI_D0
as its state argument is pci_power_up(), so the code carrying out
transitions into D0 can be put directly into that function.

Accordingly, move the code handling transitions from low-power states
into D0 directly into pci_power_up() and rename the remaining part
of pci_raw_set_power_state() to pci_set_low_power_state(), because
it only handles transitions into low-power state now.

While at it, fix up some white space, update some comments and modify
messages printed by pci_power_up() and pci_set_low_power_state() to
be less confusing (which is the only expected functional impact of
this change).

Link: https://lore.kernel.org/r/13038676.uLZWGnKmhe@kreacher
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>