Add READ_VOICEMAIL permission to privapp-permissions.

For packages don't have READ_VOICEMAIL permission, CallLogProvider will
limit its access to voicemails by applying strict grammar check. Add
this permission to CallLogBackupAgent to avoid exception when backup and
restore.

Bug: 184244328
Test: Manually restore the device
Change-Id: I7848a6b58f4502d4dd9a346e5e3725e5d741c02f