MTS Gambit - remove serial flow control

Plus protect serial flow in the common k64f code, as not all targets provide its
support.

Author: 0xc0170

hal/targets.json

@@ -575,7 +575,7 @@
         "is_disk_virtual": true,
         "macros": ["CPU_MK64FN1M0VMD12", "FSL_RTOS_MBED", "TARGET_K64F"],
         "progen": {"target": "mts-gambit"},
-        "device_has": ["I2C", "I2CSLAVE", "INTERRUPTIN", "PORTIN", "PORTINOUT", "PORTOUT", "RTC", "SERIAL", "SERIAL_FC", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"]
+        "device_has": ["I2C", "I2CSLAVE", "INTERRUPTIN", "PORTIN", "PORTINOUT", "PORTOUT", "RTC", "SERIAL", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES"]
     },
     "HEXIWEAR": {
         "inherits": ["Target"],

hal/targets/hal/TARGET_Freescale/TARGET_KSDK2_MCUS/TARGET_MCU_K64F/serial_api.c

@@ -280,6 +280,8 @@ void serial_break_clear(serial_t *obj) {
     uart_addrs[obj->index]->C2 &= ~UART_C2_SBK_MASK;
 }
 
+#if DEVICE_HAS_SERIAL_FC
+
 /*
  * Only hardware flow control is implemented in this API.
  */
@@ -314,3 +316,5 @@ void serial_set_flow_control(serial_t *obj, FlowControl type, PinName rxflow, Pi
 }
 
 #endif
+
+#endif