CHROMIUM: config: Disable USB audio.

CHROMIUM: config: Disable USB audio.

We don't support this yet.  With it enabled, the behavior of the
system is random, often getting to a state where no audio is output
when booted with a USB device attached.  Turn off for R19, will
re-enable when full USB device support is merged for R20.

BUG=chrome-os-partner:8412, chromium-os:20085
TEST=build and run kernel on stumpy/lumpy/alex, plug and unplug audio devices.

Change-Id: I79a761120e5840a85f512f5583f8c1fd6d99e665
Signed-off-by: Dylan Reid <dgreid@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/18665
Reviewed-by: Taylor Hutt <thutt@chromium.org>
Reviewed-by: Sameer Nanda <snanda@chromium.org>