Android: Improve performance when dragging flickables

If you run the Cinematic Experience demo on e.g. a Nexus 7, and try keeping your finger locked on the surface as you are dragging, you will see it drop to single-digit fps, while it's flicking at 60 if you remove your finger after flicking. Stock Android apps have similar issues, though not as bad.

We have to see if there's anything we can do to improve this. When running the proof of concept port of Qt 5 on a Asus Transformer TF300 earlier, the performance was better, so we can try to see how the two ports differ.