Fix the NPE crash when device reboot with hide cutout set

1. Set initial values to the fields.
2. Also listen to onDisplayAdded for the case that only the
   onDisplayAdded is being called after reboot.

Bug: 220884764
Test: 1. Go Settings > System > Developer option > Display cutout
      2. Select Rednder apps below cutout area
      3. Reboot device
Change-Id: I35ba3dcebcded19373901b88f7bb208633587392