pm: device: add driver init helper

Adds a helper function for initializing devices into the expected power
state, through the devices `pm_device_action_cb_t`. This eliminates code
duplication between the init functions and the PM callback.

The expected device states in order of priority are:
 * No power applied to device, `OFF`
 * `zephyr,pm-device-runtime-auto` enabled, `SUSPEND`
 * Otherwise, `ACTIVE`

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>