DisplayEventDispatcher: optimize binder calls

Use DisplayEventReciever::setVsyncRate instead of
DisplayEventReciever::requestNextVsync to accommodate a one-time
registration to vsync events when the app registers back to back
callbacks. With this approach we can save all the binder calls during
a running animation.

Test: run TouchLatency test app and observe systrace
Bug: 162096692
Change-Id: Ib415f2aade40a3d23a2b4c77e5746e5e13666d23