ARM: Dove: Add the audio device to the Cubox DT

This patch activates the audio device of the Cubox.

The audio flow (pin mpp_audio1) is output on both I2S and S/PDIF.

The third si5351 clock (#2, pin mpp13) is used as the external clock.

Signed-off-by: Jean-Francois Moine <moinejf@free.fr>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>