ART: Move oat_data_flow_attributes_ to private and put an API

The oat_data_flow_attributes had no checking mechanism to ensure bound
 correctness.

This fix handles this and also offers two functions to retrieve the
 attributes: using the MIR and DecodedInstruction.

Change-Id: Ib4f1f749efb923a803d364a4eea83a174527a644
Signed-Off-By: Jean Christophe Beyler <jean.christophe.beyler@intel.com>
diff --git a/compiler/dex/mir_optimization_test.cc b/compiler/dex/mir_optimization_test.cc
index 40ced70..891d9fb 100644
--- a/compiler/dex/mir_optimization_test.cc
+++ b/compiler/dex/mir_optimization_test.cc
@@ -172,7 +172,7 @@
       mir->offset = 2 * i;  // All insns need to be at least 2 code units long.
       mir->width = 2u;
       mir->optimization_flags = 0u;
-      merged_df_flags |= MIRGraph::oat_data_flow_attributes_[def->opcode];
+      merged_df_flags |= MIRGraph::GetDataFlowAttributes(def->opcode);
     }
     cu_.mir_graph->merged_df_flags_ = merged_df_flags;