ARM: dts: stm32: configure i2c5 support on stm32mp15xx-dkx

Configure I2C5 on stm32mp15 DK boards. It's available and can be used on:
- Arduino connector
- GPIO expansion connector
Keep it disabled by default, so the pins are kept in their initial state to
lower power consumption. This way they can also be used as GPIO.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Alain Volmat <alain.volmat@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>