Exclude ThreadX appliction

Exclude ThreadX application if the NPU driver was not compiled into
the project.

Change-Id: I036443b4c2bb276152acb7ec3267580a06d2d901
diff --git a/applications/threadx_demo/CMakeLists.txt b/applications/threadx_demo/CMakeLists.txt
index 34051f8..dbc56d2 100644
--- a/applications/threadx_demo/CMakeLists.txt
+++ b/applications/threadx_demo/CMakeLists.txt
@@ -17,7 +17,7 @@
 #
 
 # Exclude this app if ThreadX target does not exist
-if (NOT TARGET threadx)
+if (NOT TARGET threadx OR NOT TARGET ethosu_core_driver)
     message("Skipping ThreadX application")
     return()
 endif()