Floss: define MMC DBus service proto

In this patch, we define |CodecInitRequest| as |CodecInit|
input that contains config parameters. |CodecInitResponse| is
|CodecInit| output that contains generated socket token and
input frame size accepted by the codec server.

Bug: 285999597
Tag: #floss
Test: m - None
Change-Id: I273747d534623fe6ebd25468dea87254ff67de7b