ARM: DT: STiH407: Add i2s_in pinctrl configuration

This patch adds the pinctrl config for the i2s_in pins
used by the uniperif reader 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>