Floss: Define D-Bus projection for Suspend API in btmanagerd

For powerd integration, btmanagerd needs to communicate with
btadapterd's Suspend API. This CL prepares the D-Bus projection
definition for it.

Bug: 224606285
Tag: #floss
Test: Manual - build.py

Change-Id: Ieae1a88257ebf2ddccd613114b832c07026e79ff