output drivers: add option to generate a separate output range reversing param

Makes it a bit easier to configure. Reversing by setting MIN > MAX is still
supported.

src/lib/mixer_module/mixer_module.cpp

@@ -138,6 +138,9 @@ void MixingOutput::initParamHandles()
 		snprintf(param_name, sizeof(param_name), "%s_%s%d", _param_prefix, "FAIL", i + 1);
 		_param_handles[i].failsafe = param_find(param_name);
 	}
+
+	snprintf(param_name, sizeof(param_name), "%s_%s", _param_prefix, "REV");
+	_param_handle_rev_range = param_find(param_name);
 }
 
 void MixingOutput::printStatus() const
@@ -230,6 +233,12 @@ void MixingOutput::updateParams()
 			}
 		}
 
+		int32_t rev_range_param;
+
+		if (_param_handle_rev_range != PARAM_INVALID && param_get(_param_handle_rev_range, &rev_range_param) == 0) {
+			_reverse_output_mask |= rev_range_param;
+		}
+
 		if (function_changed) {
 			_need_function_update = true;
 		}

src/lib/mixer_module/mixer_module.hpp

@@ -346,6 +346,7 @@ private:
 	bool _has_backup_schedule{false};
 	const char *const _param_prefix;
 	ParamHandles _param_handles[MAX_ACTUATORS];
+	param_t _param_handle_rev_range{PARAM_INVALID};
 	hrt_abstime _lowrate_schedule_interval{300_ms};
 	ActuatorTest _actuator_test{_function_assignment};
 	uint32_t _reversible_mask{0}; ///< per-output bits. If set, the output is configured to be reversible (motors only)