SITL: Adding GPS types for Swift Binary Protocol

libraries/SITL/SITL.h

@@ -40,7 +40,8 @@ public:
         GPS_TYPE_MTK16 = 3,
         GPS_TYPE_MTK19 = 4,
         GPS_TYPE_NMEA  = 5,
-        GPS_TYPE_SBP   = 6
+        GPS_TYPE_SBP   = 6,
+        GPS_TYPE_SBP_RTK = 7,
     };
 
 	struct sitl_fdm state;