display: state-transition: Remove update_display_time()

display: state-transition: Remove update_display_time()

display states can have various timeout values depending on the policy.
update_display_time() was used for updating timeout values
accoring to the priority.

In this context, display state transition occurs after a "timeout".

This function is added below display-state-transition.
void display_state_transition_update_display_state_timeout_by_priority(void);
-> This updates timeout values depending on the policy.
1. If there are custom timeout values, then updates to that values.
2. If lockscreen is being displayed,
   then the screen timeout value will be set to lock_screen_timeout.
3. Lastly, timeout value will be set to default setting value.

To support this, getter/setter is added for specific timeout values.

Change-Id: I6cf483f17402948546d364a172334a95890238c5
Signed-off-by: Yunhee Seo <yuni.seo@samsung.com>