floss: Add Enhanced Call Status support

Enhanced Call Status is mandatory for HFP. Add it to the build flag.
Also add codes to follow ChromeOS's existing behavior to send out
commands setting the call status and speaker volume for HFP.

Tag: #floss
Bug: 213408429
Test: Build, flush and verify the commands on btmon
BYPASS_LONG_LINES_REASON: Bluetooth likes 120 char lines

Change-Id: I05acf735d6a7fc170a74fa2bde545090893fb4f7