drm/msm/sde: avoid connector pre_kickoff from disable

drm_bridge_disable called from display thread but
called before current frame transfer complete. A
pre_kickoff on dsi/dp call during this will may
changed the non-double buffered DSI registers. This
may keep MDP vs DSI out of sync for ROI configuration.
This patch avoids pre_kickoff call from connector
to avoid programming race condition.

Change-Id: Ie105a412ad37098698b208b580be832118a8f3a2
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>