Add inject-task-next-reboot debug command.

Support a debug command that will inject a fake remote task for
testing on next reboot with specified latency. This is used to
simulate the situation when a remote task arrives while the device
is not booted up and the task will be delivered once the device
boots up.

Test: Manually test on seahawk.
Bug: 275880463
Change-Id: I6eb064893bea0700da80dfa2dcf3079ddb0b59a1