Download CMSIS for ref kernels as well for cortex_m_generic (#2525)

BUG=https://github.com/tensorflow/tflite-micro/issues/2523

tensorflow/lite/micro/tools/make/targets/cortex_m_generic_makefile.inc

diff --git a/tensorflow/lite/micro/tools/make/targets/cortex_m_generic_makefile.inc b/tensorflow/lite/micro/tools/make/targets/cortex_m_generic_makefile.inc
index eace881..5aa5d25 100644
--- a/tensorflow/lite/micro/tools/make/targets/cortex_m_generic_makefile.inc
+++ b/tensorflow/lite/micro/tools/make/targets/cortex_m_generic_makefile.inc
@@ -1,4 +1,4 @@
-# Copyright 2023 The TensorFlow Authors. All Rights Reserved.
+# Copyright 2024 The TensorFlow Authors. All Rights Reserved.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -16,6 +16,16 @@
 # Generic Makefile target for ARM Cortex M builds.
 # For more info see: tensorflow/lite/micro/cortex_m_generic/README.md
 
+# Needed in case running without OPTIMIZED_KERNEL_DIR=cmsis_nn.
+CMSIS_DEFAULT_DOWNLOAD_PATH := $(DOWNLOADS_DIR)/cmsis
+CMSIS_PATH := $(CMSIS_DEFAULT_DOWNLOAD_PATH)
+ifeq ($(CMSIS_PATH), $(CMSIS_DEFAULT_DOWNLOAD_PATH))
+  DOWNLOAD_RESULT := $(shell $(MAKEFILE_DIR)/ext_libs/cmsis_download.sh $(DOWNLOADS_DIR) $(TENSORFLOW_ROOT))
+  ifneq ($(DOWNLOAD_RESULT), SUCCESS)
+    $(error Something went wrong with the CMSIS download: $(DOWNLOAD_RESULT))
+  endif
+endif
+
 FLOAT := soft
 GCC_TARGET_ARCH := $(TARGET_ARCH)