drm/msm/sde: update rotate fetch for video mode

Update the rotator prefetch value and associated flush mask
correctly for video mode. This allows the inline rotator
to be enabled/disabled on a frame to frame basis for video
mode panels.

CRs-Fixed: 2056550
Change-Id: Ibcd6c4bf3b7b3352bd097e6929e165f25d714583
Signed-off-by: Clarence Ip <cip@codeaurora.org>