dts: arm: gigadevice: gd32f403: add support for exti
dts: arm: gigadevice: gd32f403: add support for exti

Add DT node for EXTI (External Interrupt Controller). Only line
interrupts added for now (used for GPIO interrupts).

Signed-off-by: Gerard Marull-Paretas <76c1da08be458687d0066397d08e4f7ea9894377@teslabs.com>

galak/zephyr,finikorg/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr