ARM: DT: STiH407: Add SD pinctrl config for mmc0 controller

This patch adds the missing SD pinctrl config
for mmc/sd controller 0. This is required to enable the
B2144A daughter board that exposes this controller as a sd
slot.

Signed-off-by: Nebil BEN MEFTEH <nebil.ben-mefteh@st.com>
Acked-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>