ARM: dts: msm: Add audio test device for sdm670

Add audio test device as child of load module device.
This will invoke deferred probe devices to address
sound card failure issue.

Change-Id: Ibf6c1a15ebf8b8eb114549f60d096f0e8b7819ff
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>