Build system updates

Move finding Python after the project command. This was causing
incremental CMake configurations to fail.

Moving ETHOSU_TARGET_* variables after adding the common subdirectory.
It is necessary to set the variables before the core driver is
included.

Change-Id: I1c6883061cb9247336f8b33d82d2e2de870634fa
diff --git a/applications/trustzone_inference/CMakeLists.txt b/applications/trustzone_inference/CMakeLists.txt
index a985437..5a99129 100644
--- a/applications/trustzone_inference/CMakeLists.txt
+++ b/applications/trustzone_inference/CMakeLists.txt
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2021 Arm Limited. All rights reserved.
+# Copyright (c) 2021-2022 Arm Limited. All rights reserved.
 #
 # SPDX-License-Identifier: Apache-2.0
 #
@@ -16,7 +16,7 @@
 # limitations under the License.
 #
 
-if (NOT ${ETHOSU_TARGET} STREQUAL "corstone-300" OR NOT TARGET ethosu_core_driver)
+if (NOT ${ETHOSU_TARGET} STREQUAL "corstone-300" OR NOT TARGET ethosu_core_driver OR NOT ETHOSU_TARGET_NPU_CONFIG STREQUAL "ethos-u55-128")
     return()
 endif()