Adding hooks into the idle loop so HALs can execute 2nd plane tasks, such as...

Adding hooks into the idle loop so HALs can execute 2nd plane tasks, such as serving SD card read/writes requested from the USB MSD layer

Marlin/src/Marlin.cpp

@@ -548,6 +548,10 @@ void idle(
       lastUpdateMillis = millis();
     }
   #endif
+
+  #ifdef HAL_IDLETASK
+    HAL_idletask();
+  #endif
 }
 
 /**