greybus: gb-audio: Add I2C device for rt5647 codec

Add the I2C device node for the rt5647 codec.

Eventually, this will be done automatically somewhere
else but for now its done in the audio driver.

Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Acked-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>