some renaming and tweaks for linux serial driver

src/fsfw_hal/linux/CMakeLists.txt

@@ -5,11 +5,14 @@ endif()
 target_sources(${LIB_FSFW_NAME} PRIVATE UnixFileGuard.cpp CommandExecutor.cpp
                                         utility.cpp)
 
+if(FSFW_HAL_LINUX_ADD_LIBGPIOD)
+  add_subdirectory(gpio)
+endif()
+if(FSFW_HAL_LINUX_ADD_SERIAL_DRIVERS)
+  add_subdirectory(serial)
+endif()
+
 if(FSFW_HAL_LINUX_ADD_PERIPHERAL_DRIVERS)
-  if(FSFW_HAL_LINUX_ADD_LIBGPIOD)
-    add_subdirectory(gpio)
-  endif()
-  add_subdirectory(uart)
   # Adding those does not really make sense on Apple systems which are generally
   # host systems. It won't even compile as the headers are missing
   if(NOT APPLE)