hwc/overlay: Fix dma mode design and issues.

Add support for tracking the mode in which DMA is being used in overlay.
Remove unnecessary tracking variables, and their set,reset inconsistency.

With such varibles in hwc, it still leads to overlay giving out DMA pipes.
Make overlay as the single tracking place.

Change-Id: Ib949f3d0ef5918ef323c81cb1768b68a68c83da4
6 files changed