hwc2: Add support to set powerstate asynchronously.

-- Create dummy displays for all displays that support async update.
-- Map real and dummy displays as part of HWC Init.
-- Upon call from client route all calls to dummy displays. This includes
   layerstack operations ie; create, destroy, get/set params etc.
-- Post powerstate, get the current layerstack from dummy display
   and update it onto real display.

Change-Id: Ib6ab3b31e28cbc9f609933eaece940a6b9eee3ba
CRs-fixed: 2462204
13 files changed