CRAS: board_config - Add flag to disable HW echo ref

For cases when HW provided echo reference is not stable,
add a board config flag to prevent APM from using it.

Note that as we implement possibly_enable_echo_reference()
in cras_iodev_list, the echo ref will still be opened.
Just that APM doesn't use it and switches back to use the
playback device for echo cancellation processing.

BUG=b:192531773
TEST=Manual. YouTube playback works.

Change-Id: I341470fdb1c5a4c31839df1fee1c9f95b4bf3782
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/3001093
Commit-Queue: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
(cherry picked from commit 8bb1251d4c0fbd052501f55200a335d92aba0ef3)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/3007634
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
7 files changed