disp: msm: dp: take port refcount for MST sim ports

The single "port" refcount has been split in 2 on 5.4.  MST sim
layer is only getting the topology refcount but never initializes
or obtains references for the memory allocated for this port.
Add the new refcount logic required on 5.4 to MST sim layer.

Change-Id: I6e25c048fa26352c4fb718996514a1ca91432408
Signed-off-by: Steve Cohen <cohens@codeaurora.org>
Signed-off-by: Rajkumar Subbiah <rsubbia@codeaurora.org>