drm/msm/dpu: remove unwanted encoder type mapping

This change gets rid of unwanted connector-encoder type
mapping used for dsi-staging driver. Now that DPU will
be using upstream DSI driver, remove the stale code.

Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>