modules: openthread: Synchronize openthread platform with Zephyr

Updated modules/openthread/platform after latest changes in
Zephyr.

Aligned openthread implementation to the new approach.

Signed-off-by: Arkadiusz Balys <[email protected]>

Author: ArekBalysNordic

modules/openthread/CMakeLists.txt

@@ -274,6 +274,13 @@ zephyr_link_libraries(${ot_libs})
 
 endif()
 
+# Create a library for the OpenThread Zephyr utils
+zephyr_library_named(openthread_utils)
+zephyr_library_sources(
+  openthread.c
+)
+zephyr_library_sources_ifdef(CONFIG_OPENTHREAD_SHELL shell.c)
+
 add_subdirectory(platform)
 
 endif()