Gpu bufferfield fix

Some small changes in the calculation of the field sizes to allow only buffered fields as well as only absolute access fields. This is needed to allow AA-pattern and communication hiding for sparse kernels (ListLBM)

pystencils/gpucuda/kernelcreation.py

@@ -34,7 +34,7 @@ def create_cuda_kernel(assignments: Union[AssignmentCollection, NodeCollection],
     all_fields = fields_read.union(fields_written)
     read_only_fields = set([f.name for f in fields_read - fields_written])
 
-    buffers = set([f for f in all_fields if FieldType.is_buffer(f) or FieldType.is_custom(f)])
+    buffers = set([f for f in all_fields if FieldType.is_buffer(f)])
     fields_without_buffers = all_fields - buffers
 
     field_accesses = set()