Add TFLM arena allocator

Updating tflite_micro.cmake to include the arena allocator.

Change-Id: I793353afeccdf7f8a791b0e7202078eaffe72d7d
diff --git a/tflite_micro.cmake b/tflite_micro.cmake
index fea4e1a..a93bf33 100644
--- a/tflite_micro.cmake
+++ b/tflite_micro.cmake
@@ -167,6 +167,7 @@
 
 tensorflow_target_sources_glob(tflu GLOB TRUE
     ${TFLU_PATH}/*.cc
+    ${TFLU_PATH}/arena_allocator/*.cc
     ${TFLU_PATH}/memory_planner/*.cc
     ${TFLU_PATH}/kernels/*.cc)