yaml: Adding interface files

Adding 3 interfaces:
- Checkpoint
- Duration
- Statistic

Those yaml files will be used for generating dbus interface source code
files by the script under `gen/`.
It's unneeded for yocto build. However, presubmit build needs these
files to be existed since those interfaces are not merged to OpenBMC
yet.

Tested: Buildable
Google-Bug-Id: 296530445
Change-Id: Ida49772ff542456e1324e45583ab56c89ff3b11c
Signed-off-by: Michael Shen <gpgpgp@google.com>