cli: add a command to test the audio driver

This CLI command allows to invoke audio function from the depthcharge
command prompt.

BRANCH=storm
BUG=chrome-os-partner:27830
TEST=ran the below CLI commands, observed expected audio output:

    audio 100 100
    audio 1000 5000

Change-Id: I5976d24382d3618b953e3af4a2f0be9776051e89
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/239590
2 files changed