drivers: interrupt_controller: initial support for GD32 EXTI

Add initial support for the GigaDevice External Interrupt Controller.
This driver is required to manage GPIO interrupts. Only EXTI lines 0 to
15 are supported for now (no LVD, RTC, etc.). Driver can be extended in
the future to add support for extra EXTI lines.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>
diff --git a/drivers/interrupt_controller/Kconfig b/drivers/interrupt_controller/Kconfig
index 706aaa2..bbabc35 100644
--- a/drivers/interrupt_controller/Kconfig
+++ b/drivers/interrupt_controller/Kconfig
@@ -75,4 +75,6 @@
 
 source "drivers/interrupt_controller/Kconfig.eclic"
 
+source "drivers/interrupt_controller/Kconfig.gd32_exti"
+
 endmenu