1. add interface VARenderDevice for output the video into an external device when the WM is not aware of it
    2. add interface VARenderMode for APP to swith between overlay and GPU post-processing
    3. add VADisplayAttribOverlayColorKey/VADisplayAttribOverlayAutoPaintColorKey which is simliar to Xv for overlay post-processing
    4. fix the build issue on Android 2.3
Signed-off-by: Austin Yuan <shengquan.yuan@gmail.com>
Signed-off-by: Jason Hu <jason.hu@intel.com>
Signed-off-by: Zhaohan Ren <zhaohan.ren@intel.com>