Fix default app notification locking on new devices

- Fresh devices, no restore, create app prefs if app hasn't done
it already
- Apply app level locking to channels created via readxml on restore

Test: atest, factory reset device and verify that default dialer app is
locked without requiring a reboot. restore backup and verify that it's
still locked
Fixes: 127855529

Change-Id: Ieca3e064eb5b5aa5877a4b575bf6223f62259668