gs_watchdogd: add shutdown critical option

Watchdogd should be alive to complete shutdown
safely. This also aligns the behavior with previous
watchdogd.

Bug: 267080705
Test: boot
Change-Id: Iad85a0d730d032ae57530e0aa6965e2123488b2f
Signed-off-by: Martin Liu <liumartin@google.com>
1 file changed