[sam] Added empty Serial::begin() with options for CDC-ACM

See #1563

Author: cmaglie

hardware/arduino/sam/cores/arduino/USB/CDC.cpp

@@ -149,6 +149,10 @@ void Serial_::begin(uint32_t baud_count)
 {
 }
 
+void Serial_::begin(uint32_t baud_count, uint8_t config)
+{
+}
+
 void Serial_::end(void)
 {
 }

hardware/arduino/sam/cores/arduino/USB/USBAPI.h

@@ -49,6 +49,7 @@ class Serial_ : public Stream
 	RingBuffer *_cdc_rx_buffer;
 public:
 	void begin(uint32_t baud_count);
+	void begin(uint32_t baud_count, uint8_t config);
 	void end(void);
 
 	virtual int available(void);