Fix an issue is SF that caused drawing artifacts when hwc changed mode

we were not redrawing and/or clearing the FB properly when
hwc moved a layer from/to FB to/from OVERLAY.

In these cases we needed to expand the dirty region to include
the layer that changed mode.

Also split composeSurfaces() which was becoming quite large.

Change-Id: Id6fa1acfc4ff694037fddf7efd037a4405732073