Move the `pm_device_runtime_init_*` functions from <pm/device_runtime.h>
to <pm/device.h>. The initial device state should be settable
independently of whether `CONFIG_PM_DEVICE_RUNTIME` is enabled.
This also resolves a compilation error when attempting to use these
functions without also including <pm/device.h>.
Function documentation is also updated to be more general than only
referencing runtime PM, as this also applies to system PM and manually
run actions.
Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>
6d1a08b3a8