AP_IOMCU: prevent internal error on bootloader flash

when we flash the bootloader on boards with an IOMCU we expect a long
delay as the CPU stops during the flash

libraries/AP_IOMCU/AP_IOMCU.cpp

@@ -1016,8 +1016,12 @@ void AP_IOMCU::check_iomcu_reset(void)
     }
     uint32_t dt_ms = reg_status.timestamp_ms - last_iocmu_timestamp_ms;
     uint32_t ts1 = last_iocmu_timestamp_ms;
+    // when we are in an expected delay allow for a larger time
+    // delta. This copes with flash erase, such as bootloader update
+    const uint32_t max_delay = hal.scheduler->in_expected_delay()?5000:500;
     last_iocmu_timestamp_ms = reg_status.timestamp_ms;
-    if (dt_ms < 500) {
+
+    if (dt_ms < max_delay) {
         // all OK
         return;
     }