msm: mdss: fix pipe programming with dual mixer single DSI CMD mode

In command mode panels, ROIs are manipulated differently based on
multiple factors like source split enabled or not, actual ROI, single
layer mixer, dual layer mixer, single DSI or Dual DSI. Current
implementation doesn't handle dual mixer single DSI configuration
correctly which results in pipeline hang when scaling is enabled. Fix
this by adding a check about this configuration.

Change-Id: Ie4a96948a280450c8f1f0638a55aa06f26063c38
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>