More MIPS support

Working through the unimps.

Change-Id: Ie088d2061ca9a77f42ebd75e2936159465deed10
diff --git a/src/compiler/codegen/MethodCodegenDriver.cc b/src/compiler/codegen/MethodCodegenDriver.cc
index a1eeeae..42dae0f 100644
--- a/src/compiler/codegen/MethodCodegenDriver.cc
+++ b/src/compiler/codegen/MethodCodegenDriver.cc
@@ -102,11 +102,7 @@
     if (DISPLAY_MISSING_TARGETS) {
         genShowTarget(cUnit);
     }
-#if defined(TARGET_MIPS)
-    UNIMPLEMENTED(WARNING) << "Need to handle common target register";
-#else
-    opReg(cUnit, kOpBlx, rLR);
-#endif
+    opReg(cUnit, kOpBlx, rINVOKE_TGT);
     oatClobberCalleeSave(cUnit);
 }