LinuxKPI: add skeleton pci_enable_wake()

Given we do not yet support "wake" bits in device there is little need
doing it in PCI if we cannot check if we are supposed to do the
operation in first place. Once we would implement this, we would need
to also do the appropriate PCI (pme) checks before enabling (disabling)
it.

Reviewed by: dumbbell
Differential Revision: https://reviews.freebsd.org/D53208

(cherry picked from commit 885e8f272f7515b0325974de72d18b73318eff07)