Enable swap rectangle for surfaceflinger

swap rectangle feature can reduce composing region to improve performance,
also reduce power consumption during UI partial update, like mouse moving.

Google enabled this feature in Android 3.0 and the older versions,
but removed it now since some GPU devices have no this feature.

Add this feature back because i.mx6 GPU support swap rectangle.

Signed-off-by: Xianzhong <b07117@freescale.com>
Change-Id: If464c33bb78a6b9241f9d31bbece01cb504f2e18