[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/minidump_processor.cc

@@ -524,6 +524,10 @@ bool MinidumpProcessor::GetCPUInfo(Minidump *dump, SystemInfo *info) {
       info->cpu = "mips";
       break;
     }
+    case MD_CPU_ARCHITECTURE_MIPS64: {
+      info->cpu = "mips64";
+      break;
+    }
 
     default: {
       // Assign the numeric architecture ID into the CPU string.