Add #include of mul.h (#2282)

This file references Register_MUL(), which is defined in mul.h. CI complains that mul.h wasn't included directly. Also reorder #includes in alphabetical order.

BUG=306358964
diff --git a/tensorflow/lite/micro/micro_mutable_op_resolver.h b/tensorflow/lite/micro/micro_mutable_op_resolver.h
index b2563a9..90fb270 100644
--- a/tensorflow/lite/micro/micro_mutable_op_resolver.h
+++ b/tensorflow/lite/micro/micro_mutable_op_resolver.h
@@ -29,6 +29,7 @@
 #include "tensorflow/lite/micro/kernels/ethosu.h"
 #include "tensorflow/lite/micro/kernels/fully_connected.h"
 #include "tensorflow/lite/micro/kernels/micro_ops.h"
+#include "tensorflow/lite/micro/kernels/mul.h"
 #include "tensorflow/lite/micro/kernels/pooling.h"
 #include "tensorflow/lite/micro/kernels/reduce.h"
 #include "tensorflow/lite/micro/kernels/softmax.h"