Floss: Integrate powerd Suspend/Resume API

btmanagerd acts as a client of powerd Suspend/Resume API[1], and
connects to btadapterd's Suspend API. This currently only supports a
single adapter.

[1]:
https://chromium.googlesource.com/chromiumos/platform/system_api/+/HEAD/dbus/power_manager/suspend.proto

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

Change-Id: I744d2ba536366652e9350098305b01c7cfcf61b9