pm: device: extend pm_device_driver_init() description

bool pm_device_is_powered(const struct device *dev);

/**

 * @brief Setup a device driver into the lowest valid power mode

 * @brief Move a device driver into its initial device power state.

 *

 * This helper function is intended to be called at the end of a driver

 * init function to automatically setup the device into the lowest power

 * mode. It assumes that the device has been configured as if it is in

 * @ref PM_DEVICE_STATE_OFF, or @ref PM_DEVICE_STATE_SUSPENDED if device can

 * never be powered off.

 * @details This function uses the device driver's internal PM hook to

 * move the device from the OFF state to the initial power state expected

 * by the system.

 *

 * The initial power state expected by the system is:

 *

 * - ACTIVE if CONFIG_PM_DEVICE=n or (CONFIG_PM_DEVICE=y and

 *   CONFIG_PM_DEVICE_RUNTIME=n) or (CONFIG_PM_DEVICE_RUNTIME=y and

 *   !pm_device_runtime_is_enabled(dev)).

 * - SUSPENDED if CONFIG_PM_DEVICE_RUNTIME=y and device's parent power domain is ACTIVE.

 * - OFF if CONFIG_PM_DEVICE_RUNTIME=y and device's parent power domain is SUSPENDED.

 *

 * @note This function must be called at the end of a driver's init

 * function.

 *

 * @param dev Device instance.

 * @param action_cb Device PM control callback function.