CMake: Make the application the top level CMake project

So CMake can work correctly we need to define our project before we add
dependencies, otherwise the project we depend on will be registered as
the current project.

CMakeLists.txt

@@ -9,14 +9,14 @@ set(APP_TARGET mbed-os-example-attestation)
 
 include(${MBED_PATH}/tools/cmake/app.cmake)
 
+project(${APP_TARGET})
+
 add_subdirectory(${MBED_PATH})
 
 add_executable(${APP_TARGET})
 
 mbed_configure_app_target(${APP_TARGET})
 
-project(${APP_TARGET})
-
 target_include_directories(${APP_TARGET}
     PRIVATE
         .