Set default display timeout if current value is disabled by admin.

- The display timeout dialog will only show values that are allowed by the
admin. If the current display time out is greater than the max timeout set by
admin, it becomes an invalid selection. In this case, instead of not
selecting anything, set the default to the last available item.
- move TimeoutListPreference into display package.

Change-Id: I6c88f72ff2b0afe8605800074fd4626bbb16bee0
Fixes: 110104437
Test: make RunSettingsRoboTests