stm32wl5: add EXTI support for GPIO

This patch implements working support for EXTI GPIO.

Signed-off-by: Michał Łyszczek <michal.lyszczek@bofc.pl>

--
v1 -> v2:
Suggested by: Petro Karashchenko
- change (1 << n) to (1 << (n)) in macro definition
- change 1 << X to (1 << X) in code
- fix alignment

v2 -> v3:
Suggested by: Petro Karashchenko
- I was supposed to change (1 << pin) to 1 << pin, not the other way around:)

Documentation/platforms/arm/stm32wl5/index.rst

@@ -30,14 +30,14 @@ Peripheral  Support  Notes
 ==========  =======  =====
 IRQs        Yes
 GPIO        Yes
-EXTI        No
+EXTI        Yes
 HSE         Yes
 PLL         Yes      Tested @ 48MHz
 HSI         Yes      Not tested
 MSI         Yes      Not tested
 LSE         Yes      Not tested
 RCC         Yes      All registers defined, not all peripherals enabled
-SYSCFG      Yes      All registers defined, remapping not tested
+SYSCFG      Yes      All registers defined, GPIO EXTI works, remapping not tested
 USART       Yes
 LPUART      Yes      full speed with HSE works, low power mode with LSE not implemented
 DMA         No
@@ -102,7 +102,7 @@ SYSCFG
 ------
 
 System configuration controller. Can be used to remap memory or
-manage external interrupts.
+manage GPIO multiplexer for EXTI.
 
 GPIO
 ----
@@ -123,6 +123,16 @@ IPCC
 Inter-processor communication controller. IPCC is used to exchange data
 between Cortex-M4 and Cortex-M0 CPUs.
 
+EXTI
+----
+
+Extended interrupts and event controller. Extends interrupts not provided
+by NVIC. For example, there is only one interrupt for GPIO5..9 in NVIC,
+but thanks to EXTI we can differentiate which GPIO caused interrupt. Such
+interrupt first goes through EXTI and is then forwarded to main NVIC.
+
+EXTI for gpio can be enabled via `stm32wl5_gpiosetevent` function.
+
 Supported Boards
 ================