Marking TX and RX pins for UARTSerial as NC

For default construction of the driver, it would be necessary to define
the pins. However as we don't know the correct pins, until/unless user
sets them up for us. So it makes sense to mark the pins as NC. It would
be easier to debug if the pins are set to NC if user forgot to set them
up.

Author: Hasnain Virk

features/cellular/framework/targets/QUECTEL/EC2X/QUECTEL_EC2X.cpp

@@ -20,6 +20,7 @@
 #include "PinNames.h"
 #include "AT_CellularNetwork.h"
 #include "rtos/ThisThread.h"
+#include "UARTSerial.h"
 
 using namespace mbed;
 using namespace rtos;
@@ -33,6 +34,14 @@ using namespace events;
 #define MBED_CONF_QUECTEL_EC2X_RST    NC
 #endif
 
+#if !defined(MBED_CONF_QUECTEL_EC2X_TX)
+#define MBED_CONF_QUECTEL_EC2X_TX    NC
+#endif
+
+#if !defined(MBED_CONF_QUECTEL_EC2X_RX)
+#define MBED_CONF_QUECTEL_EC2X_RX    NC
+#endif
+
 #if !defined(MBED_CONF_QUECTEL_EC2X_POLARITY)
 #define MBED_CONF_QUECTEL_EC2X_POLARITY    1 // active high
 #endif
@@ -64,7 +73,6 @@ QUECTEL_EC2X::QUECTEL_EC2X(FileHandle *fh, PinName pwr, bool active_high, PinNam
     AT_CellularBase::set_cellular_properties(cellular_properties);
 }
 
-#include "UARTSerial.h"
 CellularDevice *CellularDevice::get_default_instance()
 {
     static UARTSerial serial(MBED_CONF_QUECTEL_EC2X_TX,