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

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

Change-Id: Ib5f6d9d72e8c42f88d38e06ed504848b8fc52029
Signed-off-by: Xiaowen Wu <wxiaowen@codeaurora.org>