>Doesn't [power management] belong in struct device and/or cfattach?

I would say no, or at least "not yet": power management is by no
means universal yet, and tends to have funny "special consideration"
needs, such as "device XYZ must not be powered up within 5 seconds
of device QRS".  Until some sort of sufficiently general pattern
emerges (in 10 or 15 years? :-) ), I would hold off on attempting
to "genericize" it that far.

Chris