disp: msm: Add support for seamless panel operating mode switch

DSI display may support video mode and command mode both and it may
support transition between these two modes.
This change adds seamless transition between these two modes for DSI
display by avoiding crtc enable/disable and panel power on/off
during modeset.

Change-Id: Id7ddaef7d1f0f7cc7d52283755bad53a246adec6
Signed-off-by: Lei Chen <chenlei@codeaurora.org>