Prevent multiple calls to queryDisplayStatus

For each registered listener, the display status would be queried. This
is causing a <Give Device Power Status> message to be sent,
unnecessarily spamming the CEC network.

Refactor the method to only query device power status once, then
notifying all listeners with the value.

Test: lunch adt3-userdebug; make -j
Change-Id: I49923e6193df30c03f56740ffec432f50f38d900