floss: Register OSI functions for Floss

This patch provides a null implementation for OSI functions on Floss, so
that system responsiveness will not be affected by relevant error logs.

BUG: 254667419
Tag: #floss
Test: manual test on puff, adjust A2DP volume from UI
Change-Id: Ic2a303040b1b1b7f532de44b58bc182faa5552fe