stm32/irq: Fix IRQ_ENABLE_STATS stats config to work on all MCUs.

Only the M4 and M7 MCUs have an FPU and FPU_IRQn, and FPU_IRQn is not
always the last entry/IRQ number.

ports/stm32/irq.c

@@ -31,7 +31,7 @@
 /// \moduleref pyb
 
 #if IRQ_ENABLE_STATS
-uint32_t irq_stats[FPU_IRQn + 1] = {0};
+uint32_t irq_stats[IRQ_STATS_MAX] = {0};
 #endif
 
 /// \function wfi()

ports/stm32/irq.h

@@ -39,7 +39,12 @@
 #define IRQ_ENABLE_STATS (0)
 
 #if IRQ_ENABLE_STATS
-extern uint32_t irq_stats[FPU_IRQn + 1];
+#if defined(STM32H7)
+#define IRQ_STATS_MAX   (256)
+#else
+#define IRQ_STATS_MAX   (128)
+#endif
+extern uint32_t irq_stats[IRQ_STATS_MAX];
 #define IRQ_ENTER(irq) ++irq_stats[irq]
 #define IRQ_EXIT(irq)
 #else