HWC2: Redefine retire fence as present fence

Redefines the retire fence returned by presentDisplay to be a present
fence with more strictly defined semantics: this fence should fire
at the vsync when the frame is picked up by hardware, either for
scanout (in the case of video-mode panels) or for transfer to panel
memory (in the case of command-mode panels).

Bug: 29771461
Change-Id: Idf5f86c92a8748426cf3368242c08876a48d81dd
1 file changed