Update default DispSync offsets

Updates the default DispSync offsets to 1ms/1ms to avoid SurfaceFlinger
racing against hardware vsync on untuned video-mode panels, which can
result in a significant number of dropped frames. Also moves and
updates the documentation of the offsets, which used to live in
build/target/board/generic/BoardConfig.mk.

Bug: 30801895
Change-Id: I4cb09d840e2f16fb3d05df4d7abf58d9ba36f83b