hwc: Update redrawing

By default make use of redrawing. It will be toggled only when caching
decides there shouldn't be any. Per our priority ordering:

1) Full MDP - redraw irrelevant
2) Partial/Cached MDP - decide on redraw
3) Only Video - 1 & 2, which include video, are not possible. Redraw.
4) Fallback - Redraw.

Change-Id: I6b74a5edcf79488ede2ea9480721731f371af9c8
1 file changed