hwc: Extend partial frame update for split displays

Extends partial frame update support for split displays by calculating
changing region(ROI) independently for each half of the screen. In case of
only one half updating, display driver shuts down the DSI/MDP mixer control
of the non updating half.

Maintains two ROI's for each display. In case of Non-split
displays, only left ROI is updated.

Change-Id: I8a67fe40aac665a48b6f8a46beffb9f8027851b2
8 files changed