Hide the split-screen request for secondary display task.

Currently, we cannot support the split-screen mode on the secondary
display. To prevent confused,disallowing split-screen request on
non-primary display tasks first.

Bug: 118266305
Test: 1. Use the ActivityViewTest to launch an application on virtual display.
      2. Check if the split-screen button exist on recent app.

Change-Id: Ifa6d70a1920aa4f33d260e37a3737e102949114e