GCS_MAVLink: added MAV_SYS_STATUS_AHRS

will be used to indicate AHRS health

libraries/GCS_MAVLink/message_definitions/common.xml

@@ -393,6 +393,9 @@
                <entry value="1048576" name="MAV_SYS_STATUS_GEOFENCE">
                     <description>0x100000 geofence</description>
                </entry>
+               <entry value="2097152" name="MAV_SYS_STATUS_AHRS">
+                    <description>0x200000 AHRS subsystem health</description>
+               </entry>
           </enum>
           <enum name="MAV_FRAME">
                <entry value="0" name="MAV_FRAME_GLOBAL">