pm: cleanup pm control callback implementations

- Return -ENOTSUP if the requested state is not supported
- Remove redundant "noop style" functions.
- Use switch everywhere to handle requested state (not necessary in all
  drivers, but better take off with consistency in place after current
  changes).

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
33 files changed