This patch implements Power Domain control based on Runtime PM framework.
Each Power Domain is represented by a Power Domain device and the devices
belong to these Power Domains should be set as a child device of the Power
Domain devices. The corresponding drivers of the devices should implement
Runtime PM to control the Power Domains.

Signed-off-by: Changhwan Youn <chaos.youn at samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>