CRAS ucm: ucm flag to no create default I/O node
CRAS ucm: ucm flag to no create default I/O node

For platforms which really don't have internal audio
devices, add ucm flag to suppress the creation of a
default I/O node.

BUG=chrome-os-partner:24230
TEST=Modify UCM config for panther, set
NoCreateDefaultOutputNode=1 and NoCreateDefaultInputNode=1
and verify there's no internal speaker and mic options
appear on UI.

Change-Id: Iba390b3295dd3d52eb0b67aaeebe3765bec2aafc
Reviewed-on: https://chromium-review.googlesource.com/182587
Reviewed-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Commit-Queue: Hsinyu Chao <8b91762bdbe27d3121b311091d7ca5125e9a8df6@chromium.org>
Tested-by: Hsinyu Chao <8b91762bdbe27d3121b311091d7ca5125e9a8df6@chromium.org>

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