add SUB_BINARY_SENSOR macro (#4447)

esphome/components/binary_sensor/binary_sensor.h

@@ -19,6 +19,15 @@ namespace binary_sensor {
     } \
   }
 
+#define SUB_BINARY_SENSOR(name) \
+ protected: \
+  binary_sensor::BinarySensor *name##_binary_sensor_{nullptr}; \
+\
+ public: \
+  void set_##name##_binary_sensor(binary_sensor::BinarySensor *binary_sensor) { \
+    this->name##_binary_sensor_ = binary_sensor; \
+  }
+
 /** Base class for all binary_sensor-type classes.
  *
  * This class includes a callback that components such as MQTT can subscribe to for state changes.