[mips64] Support for mips n64

Adding remaining mips n64 support including stackwalker.

BUG=None
TEST=manually tested on Linux/Android
R=vapier@chromium.org

Review URL: https://codereview.chromium.org/1418453011 .

src/processor/stackwalker.cc

@@ -234,6 +234,7 @@ Stackwalker* Stackwalker::StackwalkerForCPU(
       break;
  
     case MD_CONTEXT_MIPS:
+    case MD_CONTEXT_MIPS64:
       cpu_stackwalker = new StackwalkerMIPS(system_info,
                                             context->GetContextMIPS(),
                                             memory, modules, frame_symbolizer);