ARM: dts: stm32: Add wakeup management on stm32mp15x UART nodes

ARM: dts: stm32: Add wakeup management on stm32mp15x UART nodes

Add EXTI lines to the following UART nodes which are used for
wakeup from CStop.
- EXTI line 26 to USART1
- EXTI line 27 to USART2
- EXTI line 28 to USART3
- EXTI line 29 to USART6
- EXTI line 30 to UART4
- EXTI line 31 to UART5
- EXTI line 32 to UART7
- EXTI line 33 to UART8

Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Link: https://lore.kernel.org/r/20210319184253.5841-6-erwan.leray@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>