Hello world application

Adding hello world application that is useful when porting the stack
to a new target platform.

Change-Id: I28ba96d9fac1489d73b84cb7940d05cf9860e4ed
diff --git a/applications/CMakeLists.txt b/applications/CMakeLists.txt
index 178fc53..4950c51 100644
--- a/applications/CMakeLists.txt
+++ b/applications/CMakeLists.txt
@@ -18,6 +18,8 @@
 
 add_subdirectory(freertos)
 
+add_subdirectory(hello_world)
+
 if (CMAKE_CXX_COMPILER_ID STREQUAL "ARMClang")
     # Only armclang supported for now
     add_subdirectory(trustzone_inference)