Merge #19446

19446: cpu/stm32: Fix periph_gpio_ll_irq r=MrKevinWeiss a=maribu

### Contribution description

This fixes a high impact typo that broke GPIO LL IRQ support on a bunch of STM32 families.

This also adds a compile time check that prevents using `SYSFG` without having `SYSFG_CLOCK` defined to prevent future issues like this.

### Testing procedure

```
make BOARD=nucleo-f429zi flash test-with-config -j16 -C tests/periph_gpio_ll
[...]
TEST SUCCEEDED
```



Co-authored-by: Marian Buschsieweke <marian.buschsieweke@ovgu.de>

cpu/stm32/periph/gpio_ll_irq.c

@@ -84,10 +84,8 @@
 #ifdef RCC_APB2ENR_SYSCFGCOMPEN
 #  define SYSFG_CLOCK           APB2
 #  define SYSFG_ENABLE_MASK     RCC_APB2ENR_SYSCFGCOMPEN
-#endif
-
-#ifdef  RCC_APBENR2_SYSCFGEN
-#  define SYSFG_ENABLE_MASK     RCC_APBENR2_SYSCFGEN
+#elif defined(RCC_APB2ENR_SYSCFGEN)
+#  define SYSFG_ENABLE_MASK     RCC_APB2ENR_SYSCFGEN
 #  ifdef APB12
 #    define SYSFG_CLOCK         APB12
 #  else
@@ -106,6 +104,9 @@
 
 #ifdef SYSCFG_EXTICR1_EXTI0
 #  define EXTICR_REG(num)       (SYSCFG->EXTICR[(num) >> 2])
+#  ifndef SYSFG_CLOCK
+#    error "SYSFG_CLOCK not defined, but EXTICR reg is in SYSFG"
+#  endif
 #endif
 
 #ifdef AFIO_EXTICR1_EXTI0