boards/arduino-due: added Arduino DAC pin mapping

boards/arduino-due/include/arduino_pinmap.h

@@ -132,6 +132,14 @@ extern "C" {
 #define ARDUINO_A11             ADC_LINE(13)
 /** @} */
 
+/**
+ * @name    Mapping of Arduino DAC pins to RIOT DAC lines
+ * @{
+ */
+#define ARDUINO_DAC0            DAC_LINE(0)
+#define ARDUINO_DAC1            DAC_LINE(1)
+/** @} */
+
 #ifdef __cplusplus
 }
 #endif