HAL_ChibiOS: improve reliability of reboot

libraries/AP_HAL_ChibiOS/Scheduler.cpp

@@ -245,11 +245,11 @@ void Scheduler::reboot(bool hold_in_bootloader)
     // till the sensor buses are idle
     Shared_DMA::lock_all();
 
-    // delay to ensure the async force_saftey operation completes
+    // disable interrupts
-    delay(500);
+    disable_interrupts_save();
 
-    // disable interrupts during reboot
+    // wait for 1ms to ensure all pending DMAs are complete
-    chSysDisable();
+    delay_microseconds(1000);
 
     // reboot
     NVIC_SystemReset();