sdm: Handle secure display/camera with external display

1. Define interface to notify start/end of secure display session
2. Do dim layer commit on any flush or null commit during secure
   display session
3. Handle external/virtual display connect/disconnect during secure
   display/camera.
4. Pause virtual display during secure display/camera and pause
   external display during secure display.

Change-Id: Ie50b46044d26c50a660d5098cfa02a34cf005382
CRs-Fixed: 2181274
25 files changed