ARM: STi: DT: STiH407: Add a cec0 pin definition

This pin setup provides the correct configuration in order to
interact with the CEC HW.

Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Signed-off-by: Nicolas Vanhaelewyn <nicolas.vanhaelewyn@st.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>