Set debug.sf.latch_unsignaled=1 is used to allow surfaceflinger to
latch unsignal buffers that can give more time for buffer to render.
But if the buffer takes longer time to finish, it will block whole
display pipeline result to jank.

Bug: 157964883
Test: scrolling, launch
Change-Id: I56c3e05921de5fc9569bf3f93fde03022a64b6a4