intel: rework command buffer workarounds

Add a missing workaround, and add wa_flags so that a workaround is not emitted
more than necessary.
diff --git a/icd/intel/cmd.h b/icd/intel/cmd.h
index 16049b9..effb6aa 100644
--- a/icd/intel/cmd.h
+++ b/icd/intel/cmd.h
@@ -84,6 +84,8 @@
 
         const struct intel_ds_view *ds;
     } att;
+
+    uint32_t wa_flags;
 };
 
 struct intel_cmd_writer {