Chameleon: Add HDMI audio support

1. On client side, AudioUtility is added to provide API to control audio
function on DUT through xmlrpc server.
2. On server side, AudioClient is added to control audio function on DUT
through xmlrpc proxy.
3. Audio method is added to ChameleonPort and ChameleonTest to control
audio function on Chameleon through chameleond proxy.

BUG=chromium:398806
TEST=This patch will be used in the upcoming audiovideo_AudioBasicHDMI
test.

Change-Id: If69a4505a384ae9e2d6a0fb8b15f39338bca4be7
Reviewed-on: https://chromium-review.googlesource.com/215872
Reviewed-by: Hung-ying Tyan <tyanh@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
6 files changed