T4 SerialX - SerialX.end() and define Event callbacks

Put in first pass at SerialX.end(),
Which should disable the Serial object, and I believe set the IO pins to be GPIO pins.

Also defined the extern void SerialEvent1() like functions in header in preperation for callbacks...

teensy4/HardwareSerial.cpp

 
 void HardwareSerial::end(void)
 {
+	if (!(hardware->ccm_register & hardware->ccm_value)) return;
+	while (transmitting_) yield();  // wait for buffered data to send
+	port->CTRL = 0;	// disable the TX and RX ...
+
+	// Not sure if this is best, but I think most IO pins default to Mode 5? which appears to be digital IO? 
+	*(portConfigRegister(hardware->rx_pin)) = 5;
+	*(portConfigRegister(hardware->tx_pin)) = 5;
+
+
+	// Might need to clear out other areas as well? 
+	rx_buffer_head_ = 0;
+	rx_buffer_tail_ = 0;
+	if (rts_pin_baseReg_) rts_deassert();
+	// 
 
 }
 

teensy4/HardwareSerial.h

 extern HardwareSerial Serial6;
 extern HardwareSerial Serial7;
 extern HardwareSerial Serial8;
-//extern void serialEvent1(void);
+extern void serialEvent1(void);
+extern void serialEvent2(void);
+extern void serialEvent3(void);
+extern void serialEvent4(void);
+extern void serialEvent5(void);
+extern void serialEvent6(void);
+extern void serialEvent7(void);
+extern void serialEvent8(void);
 
 
 #endif // __cplusplus