HAL: Serial: Add DEVICE_SERIAL_FC guards

Functions related to serial flow control should not be exposed
if DEVICE_SERIAL_FC is not defined
* serial_set_flow_control,
* serial_cts_pinmap,
* serial_rts_pinmap.

hal/serial_api.h

@@ -211,6 +211,7 @@ void serial_break_clear(serial_t *obj);
  */
 void serial_pinout_tx(PinName tx);
 
+#if DEVICE_SERIAL_FC
 /** Configure the serial for the flow control. It sets flow control in the hardware
  *  if a serial peripheral supports it, otherwise software emulation is used.
  *
@@ -220,6 +221,7 @@ void serial_pinout_tx(PinName tx);
  * @param txflow The RX pin name
  */
 void serial_set_flow_control(serial_t *obj, FlowControl type, PinName rxflow, PinName txflow);
+#endif
 
 /** Get the pins that support Serial TX
  *
@@ -239,6 +241,7 @@ const PinMap *serial_tx_pinmap(void);
  */
 const PinMap *serial_rx_pinmap(void);
 
+#if DEVICE_SERIAL_FC
 /** Get the pins that support Serial CTS
  *
  * Return a PinMap array of pins that support Serial CTS. The
@@ -256,6 +259,7 @@ const PinMap *serial_cts_pinmap(void);
  * @return PinMap array
  */
 const PinMap *serial_rts_pinmap(void);
+#endif
 
 #if DEVICE_SERIAL_ASYNCH