Add a new powervr.ini to configure the screen refresh rate

We need to configure the screen refresh rate in order to get optimum
performance without tearing from the graphics subsystem.

While we're at it, remove this file from proprietary-files.txt -- it's
not a binary blob, so it doesn't belong there.

Change-Id: I303900db4e892a23b23b5a48b18c28011faca2de