MLBEDSW-7274 Add support for Variable Tensors

Added support for Variable Tensor, including offline planning.

Change-Id: I39f33fee207f1f1a4574a0f53f7377eec8709e15
Signed-off-by: Fredrik Svedberg <fredrik.svedberg@arm.com>
diff --git a/ethosu/vela/reader_util.py b/ethosu/vela/reader_util.py
index 78eb436..d30a7bb 100644
--- a/ethosu/vela/reader_util.py
+++ b/ethosu/vela/reader_util.py
@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: Copyright 2021-2022 Arm Limited and/or its affiliates <open-source-office@arm.com>
+# SPDX-FileCopyrightText: Copyright 2021-2023 Arm Limited and/or its affiliates <open-source-office@arm.com>
 #
 # SPDX-License-Identifier: Apache-2.0
 #
@@ -56,7 +56,7 @@
 
     for tens in tensors:
         if not tens.ops:
-            op = Operation(Op.Const, tens.name)
+            op = Operation(Op.Placeholder if tens.is_variable else Op.Const, tens.name)
             op.set_output_tensor(tens)