modules: tf-m: fix Ethos-U Cmake warnings

This is to fix the below compiler warning from TF-M builds
   that don't use the Ethos-U driver.
```
CMake Warning:
  Manually-specified variables were not used by the project:

    ETHOS_DRIVER_PATH
```

Signed-off-by: Sudan Landge <sudan.landge@arm.com>

modules/trusted-firmware-m/CMakeLists.txt

@@ -253,7 +253,9 @@ if (CONFIG_BUILD_WITH_TFM)
 
   list(APPEND TFM_CMAKE_ARGS -DTFM_TESTS_REVISION_CHECKS=OFF)
 
-  list(APPEND TFM_CMAKE_ARGS -DETHOS_DRIVER_PATH=${CONFIG_TFM_ETHOS_DRIVER_PATH_LOCAL})
+  if(CONFIG_TFM_ETHOS_DRIVER_PATH_LOCAL)
+    list(APPEND TFM_CMAKE_ARGS -DETHOS_DRIVER_PATH=${CONFIG_TFM_ETHOS_DRIVER_PATH_LOCAL})
+  endif()
 
   file(MAKE_DIRECTORY ${TFM_BINARY_DIR})
   add_custom_target(tfm_cmake

modules/trusted-firmware-m/Kconfig.tfm

@@ -312,6 +312,7 @@ endchoice
 
 config TFM_ETHOS_DRIVER_PATH_LOCAL
 	string "Path to a locally available Ethos-U driver or an empty string"
+	depends on SOC_SERIES_MPS3
 	default "${ZEPHYR_HAL_ETHOS_U_MODULE_DIR}"
 	help
 	  Path to a locally available Ethos-U driver to be used for TF-M builds or