cras: Add device_config_dir argument to set config directory

If device_config_dir is set in the argument, find volume curve
configs in that directory instead of /etc/cras.

BUG=chrome-os-partner:33383
TEST=Check volume curve is still functional. The real use case of
device_config_dir will be in the next patch.
Change-Id: Ic35cd20f4d73ce1edf3b0963fa5e3621e110392a
Reviewed-on: https://chromium-review.googlesource.com/271466
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
1 file changed