ARM: dts: stm32: add UserPA13 button on stm32mp135f-dk

The PA13 user button is connected to the PA13 pin of the stm32mp135f-dk
board. It requires an internal pull-up configuration.

Signed-off-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>