[topgen] Allow data_intg_passthru key on memories

Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/util/topgen/validate.py b/util/topgen/validate.py
index 9702a5e..9bc7607 100644
--- a/util/topgen/validate.py
+++ b/util/topgen/validate.py
@@ -216,6 +216,10 @@
     'size': ['d', 'memory region size in bytes for the linker script, '
                   'xbar and RTL parameterisations'],
     'config': ['d', 'Extra configuration for a particular memory'],
+    'data_intg_passthru': [
+        'pb',
+        'Integrity bits are passed through directly from the memory'
+    ]
 }
 
 memory_added = {