stm32/storage: Add support for internal storage on Cortex-M0 MCUs.

This implements self-triggering of the Flash NVIC interrupt on Cortex-M0
devices, which allows enabling internal storage on those MCUs.

Signed-off-by: Asensio Lorenzo Sempere <asensio.aerospace@gmail.com>

ports/stm32/storage.c

@@ -83,7 +83,11 @@ uint32_t storage_get_block_count(void) {
 static void storage_systick_callback(uint32_t ticks_ms) {
     if (STORAGE_IDLE_TICK(ticks_ms)) {
         // Trigger a FLASH IRQ to execute at a lower priority
+        #if __CORTEX_M == 0
+        NVIC_SetPendingIRQ(FLASH_IRQn);
+        #else
         NVIC->STIR = FLASH_IRQn;
+        #endif
     }
 }