Restructure to reduce MIR references

This CL eliminates most of the MIR references in the lower-level
code generator.  This allows a higher level of code sharing with
the MIR->LIR and GreenlandIR->LIR lowering passes.

The invoke, launchpads and new array support will need some more
extensive refactoring (future CL).

Change-Id: I75f249268c8ac18da1dd9180ff855d5176d6c4fe
diff --git a/src/compiler/codegen/CodegenFactory.cc b/src/compiler/codegen/CodegenFactory.cc
index 3a7cb82..71b557c 100644
--- a/src/compiler/codegen/CodegenFactory.cc
+++ b/src/compiler/codegen/CodegenFactory.cc
@@ -44,7 +44,7 @@
 LIR* loadWordDisp(CompilationUnit* cUnit, int rBase, int displacement,
                   int rDest)
 {
-  return loadBaseDisp(cUnit, NULL, rBase, displacement, rDest, kWord,
+  return loadBaseDisp(cUnit, rBase, displacement, rDest, kWord,
                       INVALID_SREG);
 }
 
@@ -97,7 +97,7 @@
   } else {
     DCHECK((rlSrc.location == kLocDalvikFrame) ||
            (rlSrc.location == kLocCompilerTemp));
-    loadBaseDispWide(cUnit, NULL, rSP, oatSRegOffset(cUnit, rlSrc.sRegLow),
+    loadBaseDispWide(cUnit, rSP, oatSRegOffset(cUnit, rlSrc.sRegLow),
                      regLo, regHi, INVALID_SREG);
   }
 }