AP_HAL: added get_custom_defaults_file() to Util

libraries/AP_HAL/AP_HAL_Boards.h

@@ -417,4 +417,8 @@
 #define HAL_OS_POSIX_IO 0
 #endif
 
+#ifndef HAL_PARAM_DEFAULTS_PATH
+#define HAL_PARAM_DEFAULTS_PATH NULL
+#endif
+
 #endif // __AP_HAL_BOARDS_H__

libraries/AP_HAL/Util.h

@@ -23,6 +23,11 @@ public:
     virtual const char* get_custom_log_directory() { return NULL; } 
     virtual const char* get_custom_terrain_directory() const { return NULL;  }
 
+    // get path to custom defaults file for AP_Param
+    virtual const char* get_custom_defaults_file() const {
+        return HAL_PARAM_DEFAULTS_PATH;
+    }
+    
     // run a debug shall on the given stream if possible. This is used
     // to support dropping into a debug shell to run firmware upgrade
     // commands