ARM: STi: DT: STiH407: Add i2c3 alternate pin configs

i2c3 controller can use several sets of pins depending
on board design. This patch adds the missing alternate
pinconfigs.

Signed-off-by: Seraphin Bonnaffe <seraphin.bonnaffe@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>