ARM: dts: uniphier: add audio in/out pin-mux node

The UniPhier AIO audio system needs I2S data in/out lines
and clock signal pins to connect external codec chip.

Signed-off-by: Katsuhiro Suzuki <suzuki.katsuhiro@socionext.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>