ARM: dts: stm32: Add I2C1 support for STM32F746 eval board

This patch adds I2C1 support for STM32F746 eval board

Signed-off-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>