rc.io:Add USE_IO == yes && IO_PRESENT == yes test

On a FMU without a px4io (FMUv4, NXPhlite etc), this code should
  not be run.

ROMFS/px4fmu_common/init.d/rc.io

@@ -2,7 +2,8 @@
 #
 # PX4IO interface init script.
 #
-
+if [ $USE_IO == yes -a $IO_PRESENT == yes ]
+then
 	if px4io start
 	then
 		# Allow PX4IO to recover from midair restarts.
@@ -14,3 +15,4 @@ else
 		echo "PX4IO start failed" >> $LOG_FILE
 		tune_control play -m ${TUNE_ERR}
 	fi
+fi