mc_autotune_attitude_control: add new MC_AT_EN parameter to enable

- only enabled by default on boards that aren't memory constrained

src/modules/mc_autotune_attitude_control/mc_autotune_attitude_control_params.c

@@ -39,6 +39,14 @@
  * @author Mathieu Bresciani <mathieu@auterion.com>
  */
 
+/**
+ * Multicopter autotune module enable
+ *
+ * @boolean
+ * @group Autotune
+ */
+PARAM_DEFINE_INT32(MC_AT_EN, 0);
+
 /**
  * Start the autotuning sequence
  *