drm/msm/sde: issue LUTDMA kickoff based on ctl paths

Currently LUTDMA kickoff is triggered based on the
number of physical encoders. This might cause redundant
LUTDMA kickoffs as the physical encoders  might be driven
by a single ctl. Move this in-line with the CTL flush logic
which issues the flush based on the number of CTL paths.

Change-Id: Icc1b8cafaaa3d713a490474d72c1298ecbd02c54
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>