ARM: DT: STiH407: Add spdif_out pinctrl config

This patch adds the pinctrl config for the spidf out
pins used by the sasg codec IP.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>