bootstat: add 4 reboot reasons to known set

- reboot,rtc
- reboot,dm-verity_device_corrupted
- reboot,dm-verity_enforcing
- reboot,keys_clear

Test: none
Bug: 128929506
Bug: 128929604
Change-Id: I5438c236abb67b74c7b9d717930c0ea69f70540d
Signed-off-by: Jone Chou <jonechou@google.com>