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
Camera2: Preview needs to be stopped when changing resolution

This was done in startPreview as a hack, but was removed in
f729b85e12cfa2674048d8cce2f724014b8fc910. Specifically add it
back when the resolution is changed.

Change-Id: I306abd788bafdff4e6fba7eec4e6ff05bb3cc47c