drm/msm/sde: move rot flush config to crtc kickoff

Move the rotator flush bit determination from the blend setup
to the kickoff function. This consolidates all sbuf related
programming between sync/async/offline modes to the kickoff
function instead of splitting the configuration between blend
and kickoff functions.

Change-Id: I9b696a4f3f47a5ed699961d3b56e236a027982ff
Signed-off-by: Clarence Ip <cip@codeaurora.org>