Rename newly created internal subdir to source dir

This avoids the overlap in meaning with a strong `internal` dir which
would allow shipping the public header without the content of the
internal dir. The subirs `source` instead contain classes and APIs that
users should not use and are subject to change.

Author: hugueskamba

TESTS/mbed_drivers/timerevent/main.cpp

@@ -21,7 +21,7 @@
 #include "greentea-client/test_env.h"
 #include "unity.h"
 #include "utest.h"
-#include "drivers/internal/TimerEvent.h"
+#include "drivers/source/TimerEvent.h"
 #include "hal/ticker_api.h"
 #include "rtos.h"
 

UNITTESTS/stubs/SerialBase_stub.cpp

@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-#include "drivers/internal/SerialBase.h"
+#include "drivers/source/SerialBase.h"
 
 namespace mbed {
 

drivers/MbedCRC.h

@@ -17,7 +17,7 @@
 #ifndef MBED_CRC_API_H
 #define MBED_CRC_API_H
 
-#include "drivers/internal/TableCRC.h"
+#include "drivers/source/TableCRC.h"
 #include "hal/crc_api.h"
 #include "platform/mbed_assert.h"
 #include "platform/SingletonPtr.h"

drivers/RawSerial.h

@@ -22,7 +22,7 @@
 #if DEVICE_SERIAL || defined(DOXYGEN_ONLY)
 
 #include "mbed_toolchain.h"
-#include "drivers/internal/SerialBase.h"
+#include "drivers/source/SerialBase.h"
 #include "platform/NonCopyable.h"
 #include <cstdarg>
 

drivers/Serial.h

@@ -22,7 +22,7 @@
 #if DEVICE_SERIAL || defined(DOXYGEN_ONLY)
 
 #include "platform/Stream.h"
-#include "drivers/internal/SerialBase.h"
+#include "drivers/source/SerialBase.h"
 #include "platform/PlatformMutex.h"
 #include "platform/NonCopyable.h"
 

drivers/Ticker.h

@@ -17,7 +17,7 @@
 #ifndef MBED_TICKER_H
 #define MBED_TICKER_H
 
-#include "drivers/internal/TimerEvent.h"
+#include "drivers/source/TimerEvent.h"
 #include "platform/Callback.h"
 #include "platform/mbed_toolchain.h"
 #include "platform/NonCopyable.h"

drivers/UARTSerial.h

@@ -23,7 +23,7 @@
 #if (DEVICE_SERIAL && DEVICE_INTERRUPTIN) || defined(DOXYGEN_ONLY)
 
 #include "platform/FileHandle.h"
-#include "drivers/internal/SerialBase.h"
+#include "drivers/source/SerialBase.h"
 #include "InterruptIn.h"
 #include "platform/PlatformMutex.h"
 #include "platform/CircularBuffer.h"