Prevent buggy display orientation when exiting vr

The underlying issue is that the viewport settings were being re-set to
(0,0,-1,-1) on every transition to VR. I've instead extracted the vsync
period updates, and only apply those, as that was really all we wanted
out of it.

Bug: 37093920
Test: Compile and run Vr application. The 2d scene is now no longer in
the weird landscape viewport with portrait orientation if the phone is
in landscape when exiting VR mode.

Change-Id: I2bab6e4d834e15f477d1b56991375d1a18a77b8c