drm/msm/sde: populate primary display flag

In case of multiple encoders and DSI controllers topology,
update the corresponding display information with primary
flag so that user modules are correctly updated.

CRs-Fixed: 2254681
Change-Id: Ia1e4afda9e41466407fba3ad324e7dbf80b2e08c
Signed-off-by: Kalyan Thota <kalyant@codeaurora.org>