drm/msm/sde: add seamless dsi panel operating mode transition

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 any display by avoiding crtc enable/disable during modeset.
It creates video and command mode physical encoders respectively
to support dynamic panel operating mode switch.

Change-Id: I825702de04b728976dd081e0169bb8e0af520b7b
Signed-off-by: Lei Chen <chenlei@codeaurora.org>