binarystore: Include main.cpp in libbinarystore.so
binarystore: Include main.cpp in libbinarystore.so

main.cpp is required to register the ipmi handlers.

Without main.cpp, the phosphor-ipmi-host does not pick up the register
for the binarystore.

Tested:
```
$ systemctl restart phosphor-ipmi-host
$ journalctl | grep "Loading from config with"
ipmid[4500]: Loading from config with
```

Change-Id: Ia84b48c9680703528d26bf70c27f5799439a2fb6
Signed-off-by: Willy Tu <1e3df9bf0ac020872e0e39905eae1676fb455af4@google.com>

openbmc/phosphor-ipmi-blobs-binarystore