boot-time-blob: Implement `stat` function

`stat` function may be called first before other command to be called to
check the state.
In this case `stat` must be implemented to make that process work.

Tested:
Checked open->stat->read flow is working by internal tool.

Change-Id: I89676bf9431d77ec2a3a2b76b99ae3dcbc8a9f20
Signed-off-by: Michael Shen <gpgpgp@google.com>
1 file changed