drm/msm/sde: populate primary flag based on display type

In case of 2 encoders + 2 DSI ctrls topology, mark display
having display_type as primary to be primary in display info
else mark it as secondary.

Change-Id: Ia1e4afda9e41466407fba3ad324e7dbf80b2e08c
Signed-off-by: Tharun Raj Soma <tsoma@codeaurora.org>