Added configurable idlescreen timeout

Users will now be able to configure lux dependent idle screen timeout
values in display config. System will keep track of this value, and if
the device stays idle for the configured time, the refresh rate will be
reduced to preserve the power

Bug: 310026579
Test: atest DisplayServicesTest
Change-Id: I632329dffa59bc1e9c96bcc20ebc6cac4c90ae84