audio: add audio timer trace points

Track audio timer starts and stops.  Also trace delayed audio timer calls.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180702161524.17268-1-kraxel@redhat.com