Only create valid insets sources of display cutout

This CL only creates valid insets sources of display cutout, but not
always creates ones for all sides. Othereise, the redundant sources may
waste the performance.

Fix: 236112953
Test: adb shell dumpsys window displays
Change-Id: Idc4d8921d044652e84b946b91a2c9fb1b27c2ec0