[MLBEDSW-3891] Fix reading back in an ethos-u custom op

Fixed assertion when reading back in an ethos-u custom op.

Signed-off-by: Fredrik Svedberg <fredrik.svedberg@arm.com>
Change-Id: I275ec9187ffead1e96f2522ecbd658328fa4ef69
diff --git a/ethosu/vela/architecture_features.py b/ethosu/vela/architecture_features.py
index 33e7add..f7d5fd6 100644
--- a/ethosu/vela/architecture_features.py
+++ b/ethosu/vela/architecture_features.py
@@ -275,6 +275,8 @@
             TensorPurpose.Weights: self.permanent_storage_mem_area,
             TensorPurpose.FeatureMap: self.feature_map_storage_mem_area,
             TensorPurpose.LUT: self.permanent_storage_mem_area,
+            TensorPurpose.Scratch: self.feature_map_storage_mem_area,
+            TensorPurpose.ScratchFast: self.fast_storage_mem_area,
         }
 
         self.tensor_storage_mem_type = {
@@ -282,6 +284,8 @@
             TensorPurpose.Weights: MemType.Permanent_NPU,
             TensorPurpose.FeatureMap: MemType.Scratch,
             TensorPurpose.LUT: MemType.Scratch,
+            TensorPurpose.Scratch: MemType.Scratch,
+            TensorPurpose.ScratchFast: MemType.Scratch_fast,
         }
 
         self.min_block_sizes = {