SurfaceFlinger: Some fixes to DispSync

Pass negative offsets to DispSync to fix the scheduling
when SurfaceFlinger uses negative offsets.

Change-Id: I1f9544b064305c87f973120cc1bc59a0268b78e5
Bug: 132284303
Test: UI-Bench
(cherry picked from commit 45e4e3634e94171bca7e3df287bcbcb74df6ca4a)
Merged-In: I1f9544b064305c87f973120cc1bc59a0268b78e5
9 files changed