Send a regions-of-interest event containing a rectangle surrounding the
focus point to the camera source when the camera's focusPointMode
is QCameraFocus::CustomFocusPoint. Reset the regions-of-interest if the
focusPointMode changes to any other value.
[ChangeLog][GStreamer] Implement customFocusPoint in camerabin backend.
Change-Id: If75405733b18d476dff5467abae3f08271caf06a
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>