drm/msm/dp: add display-type support in dp

Add display-type in connector's capability blob for DP-SST.
This allows user to configure DP as primary display.

Change-Id: Ib5f6d9d72e8c42f88d38e06ed504848b8fc52029
Signed-off-by: Xiaowen Wu <wxiaowen@codeaurora.org>
Signed-off-by: Narender Ankam <nankam@codeaurora.org>
Signed-off-by: Chirag Khurana <ckhurana@codeaurora.org>