ARM: dts: stm32: Add DAC pins used on stm32mp157c-ed1

Define pins that can be used by digital-to-analog converter on
stm32mp157c eval daughter board:
- PA4 and PA5 pins are available respectively on JP11 and JP10

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