PM / devfreq: rk3399_dmc: Use the resource-managed function to add devfreq dev

This patch uses the resource-managed to add the devfreq device.
This function will make it easy to handle the devfreq device.

- struct devfreq *devm_devfreq_add_device(struct device *dev,
				  struct devfreq_dev_profile *profile,
				  const char *governor_name,
				  void *data);

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>