Use `pm_device_*` prefix for the device runtime PM API. This adds the
API to the `pm` namespace, making it clear part of the PM subsystem.
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
- Move PM related APIs to `include/pm` so that it follows API `pm_`
prefix namespace. In order to make transition easier
`include/power/power.h` is kept pointing to `include/pm/pm.h`.
- Move most of device PM related content from `include/device.h` to
`include/pm/device.h` and `include/pm/runtime.h`.
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
