Camera: fix panorama preview on older devices

When PREVIEW_FBO_WIDTH_SCALE is set to 4, the preview FBO becomes
larger than older GPUs can handle. Detect it and reduce the value
to 2 like on pre-KitKat releases.

Change-Id: I20785d157bed48816820476d066ef9d4a9f73672
Merge remote-tracking branch 'omni/android-4.4' into omni-4.4