NRF5x targets: Replace UARTSerial references with BufferedSerial

`BufferedSerial` is `UARTSerial` renamed to convey the original purpose
of the class. It is the recommended buffered I/O serial class.

Author: hugueskamba

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52832/TARGET_RIOT_MICRO_MODULE/ONBOARD_RM1000_AT.cpp

@@ -17,7 +17,7 @@
 #if MBED_CONF_NSAPI_PRESENT
 
 #include "ONBOARD_RM1000_AT.h"
-#include "UARTSerial.h"
+#include "drivers/BufferedSerial.h"
 
 #include "mbed-trace/mbed_trace.h"
 #ifndef TRACE_GROUP
@@ -140,7 +140,7 @@ CellularDevice *CellularDevice::get_target_default_instance()
 {
     tr_debug("Calling CellularDevice::get_target_default_instance from ONBOARD_RM1000_AT");
 
-    static UARTSerial serial(MDM_UART3_TXD, MDM_UART3_RXD, 230400);
+    static BufferedSerial serial(MDM_UART3_TXD, MDM_UART3_RXD, 230400);
 #if DEVICE_SERIAL_FC
     if (MDM_UART3_RTS != NC && MDM_UART3_CTS != NC) {
         tr_debug("Modem flow control: RTS %d CTS %d", MDM_UART3_RTS, MDM_UART3_CTS);

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52840/TARGET_EP_AGORA/ONBOARD_TELIT_ME910.cpp

@@ -23,7 +23,7 @@
 #include "platform/mbed_thread.h"
 #include "PinNames.h"
 
-#include "UARTSerial.h"
+#include "drivers/BufferedSerial.h"
 #include "ONBOARD_TELIT_ME910.h"
 #include "ThisThread.h"
 #include "CellularLog.h"
@@ -174,7 +174,7 @@ void ONBOARD_TELIT_ME910::onboard_modem_power_down()
 
 CellularDevice *CellularDevice::get_target_default_instance()
 {
-    static UARTSerial serial(MDMTXD, MDMRXD, 115200);
+    static BufferedSerial serial(MDMTXD, MDMRXD, 115200);
 #if DEVICE_SERIAL_FC
     if (MDMRTS != NC && MDMCTS != NC) {
         tr_debug("Modem flow control: RTS %d CTS %d", MDMRTS, MDMCTS);