AP_Button: add and use HAL_BUTTON_ENABLE

libraries/AP_Button/AP_Button.cpp

@@ -15,6 +15,9 @@
 
 
 #include "AP_Button.h"
+
+#if HAL_BUTTON_ENABLED
+
 #include <GCS_MAVLink/GCS_MAVLink.h>
 #include <GCS_MAVLink/GCS.h>
 
@@ -400,3 +403,5 @@ AP_Button &button()
 }
 
 }
+
+#endif

libraries/AP_Button/AP_Button.h

@@ -14,6 +14,14 @@
  */
 #pragma once
 
+#include <AP_HAL/AP_HAL_Boards.h>
+
+#ifndef HAL_BUTTON_ENABLED
+#define HAL_BUTTON_ENABLED 1
+#endif
+
+#if HAL_BUTTON_ENABLED
+
 #include <AP_HAL/AP_HAL.h>
 #include <AP_Param/AP_Param.h>
 
@@ -127,3 +135,5 @@ private:
 namespace AP {
     AP_Button &button();
 };
+
+#endif