Another clarifying rename and a bit more automation.

kNumDalvikInstructions is now kNumPackedOpcodes, there is a new
kMaxOpcodeValue, and both are generated by opcode-gen.

Change-Id: Ic46f1f52d2d21382452c8e777024f4a985ad31d3
Bonus: Reworded the switch and array data comment for clarity.
diff --git a/vm/compiler/CompilerIR.h b/vm/compiler/CompilerIR.h
index c83c0ba..712ca4c 100644
--- a/vm/compiler/CompilerIR.h
+++ b/vm/compiler/CompilerIR.h
@@ -78,7 +78,7 @@
 } LIR;
 
 enum ExtendedMIROpcode {
-    kMirOpFirst = kNumDalvikInstructions,
+    kMirOpFirst = kNumPackedOpcodes,
     kMirOpPhi = kMirOpFirst,
     kMirOpNullNRangeUpCheck,
     kMirOpNullNRangeDownCheck,