RC_Channel: add configured_in_storage metthod

libraries/RC_Channel/RC_Channel.h

@@ -91,6 +91,9 @@ public:
     // set and save trim if changed
     void       set_and_save_radio_trim(int16_t val) { radio_trim.set_and_save_ifchanged(val);}
 
+    // check if any of the trim/min/max param are configured in storage, this would indicate that the user has done a calibration at somepoint
+    bool       configured_in_storage() { return radio_min.configured_in_storage() || radio_max.configured_in_storage() || radio_trim.configured_in_storage(); }
+
     ChannelType get_type(void) const { return type_in; }
 
     AP_Int16    option; // e.g. activate EPM gripper / enable fence